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EARTHWORM (Pheretima Posthuma)
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External Features
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shape & size :- The body of earthworm is elongeted, narrow, cylindrical,& bilateraly symmetrical.
It has a pointed tapering anterior end more or less blunt posterior end, the body being a little behind the anterior end.
This body form is well adapted for burrowing habit. The length of the body of a mature earthworm is about 150 mm & the
breadth is 3 to 5 mm.
Colouration :- The colour of the body of Earthworm is dark brown or caly colour is due to a pigment
called prophyrin, which is derived from chlorophyll. This pigment protects the animal against harmful light rays.
Sementation :- The soft & necked body of Earthworm is metamerically divided into a series of
about 100 to 120 segments. The
external transverse groove of the body corresponds to the internal segmentation, by septum.
Peristomium :- The earthworm has no distonet head. The anterior first segment is known as peristomium
.On the ventral side of
Peristomium, there is a semilunar aperture,the mouth . The peristomium is prolonged anteriorly into a fleshy lobe, known
as
prosotomium, which overhangs the mouth.
Clitellum :- In a mature Earthworm, the 14th, 15th & 16th segments donot show any segmentation
but completely & permanently
surrounded by a thick & distinct band of glandular tissue which is called as clitellum. This ofr the formation of cocoon
or egg-capsule. The body of Earthworm can be region & clitellum to last segment is the post-clitellar region.
Seat :- About the middle of each segment there is a hing of tiny curved, rod-shaped, chitineous
bristles called as setae are the
main locomontory organs.setae are not found in first segment, clitellum(14,15 &16 segments) & the last segment.
Apertures :- The different apertures present in the body of an Earthworm are,
i) Mouth:- It is a crescentric anterior aperture lying on the ventral side of peristomium overhung by the prostomium
ii)Anus:-It is a median circular aperture situated terminally at the last anal segment.
iii)Female Genital Pores:- These are a pair of crescentric apertures of spermathecae in the grooves of 5/6,6/7, 7/8
& 8/9
segments, one on each side in Ventro lateral position.
iv)Male Genital Pores:-These are a pair of cresecentric apertures of the common prostatic & spermatic ducts open
on the ventral surface of the 18th segment, one on each side.
v)Spermathecal Pores:-These are four parts of apertures of spermathecae in the grooves of 5/6, 6/7, 7/8 & 8/9 segments,
one each side in ventrolateral position.
vi)Nephridio pores:- These are a large number of very minute openings of the integumentary nephridia, scattered all
over the body except the first two segments.
vii)Dorsal Pores:-These are minute apertures of the coelomic chambers located mid dorsally, one on each inter segmental
groove, behind the 12th segment, except the last.
Genital Papillae :- These are two pairs of distenet rounded elevations,the Genital papillae,one
pair each in the 17th & 19th segments on the ventral surface. Each papilla bears a shallow cup like depression at its
top at which the Accessory Gland opens. The papilla as a sucker during couplation.
Besides the darker colour of the dorsal side there is a distinct dorsal medion line on the dorsal side that runs longitudinally,
at mid dorsal region, from anterior to posterior end of body, this is the dorsal blood vessel.
Digestive System
The digestive system of Earthworm is well-developed & it consists of Alimentary canal. The alimentary canal lies in
the body-cavity as a straight tube that mouth to the posterior Anus. The part of Alimentary canal are as follow
1)Mouth :- The is a crescentric aperture. that lies ventral to prostomium & at the anterior edge
of peristomium or first segment.
2) Buccal Chamber :- The mouth opens into a short thin walled & narrow Buccal Chamber that extends
uoto the first third segment. its internal lining is provided with longitudinal- folds.
3)Pharynx :- The nuccal chamber leads into a wide muscular & pear-shaped buccal chamber by a
dorsal groove. the pharynx is with a narrow & dorsoventrally compressed but laterally expanded pharyngeal -cavity. it
is due to the presence of a pharyngeal- mass on its dorsal side. this pharyngeal-mass consists of chromophil (saliva-secreting)
cells, muscular-vascular tissues & ciliadeepithelium. the lateral-walls of pharyngeal-cavity into dorsal salivary chamber
& ventral conducting chamber. the chromophil cells secret salivary-secretion, containing mucus & proteolytic enxymes,
that are poured into the salivary-chamber. the muscle-strands attached to the outside of pharyngeal-cavity cause a sucling-action
to draw food into it.
4)Oesophagus :- The pharynx leads behind into a narrow thin-walled, somewhat elongated & slightly
bent Opsophagus gullet that extend upto the 7th segment,
5)Gizzard :- In the 8th segment, the oesophagus expands & modifies into a large, distinct,
avalf muscular, Gizzard. the thick internal-wall of gizzard is internally lined by internal-cutidr & externally ot consists
of cercular muscles.
6)Stomach :- The gizzard leads behind into a slightly long, somewhat wider, glandular & musculer
stomach, that runs from 9th to 14th segment. it is provide with sphincler at each end. its internal muscular & vascular
walls are thrown into transverse folds. the glandular cells secrete digestive-enzymes. in some earthworms, calciferous glaids
also found.
7)Intestine : -It is a long, wide & thin-walled behind the anterior ends. this body form
is wall adapted for burrowing habit. the lenght of the body of a mature Earthworm is about 150mm & the tube that extends
from 15th to the last segments.It has beaded appearence due to the grooves of septa. Its internal lining is vascular, glandular,
ciliated & folded.
The intestine is divisible into 3 parts.
a)Pre typhlosolsar region:-This part lies between 15th to villiwhich are highly vascular. In 26th segment,
the intestine has given out a pair of forwardly directed, lateral,conical, out-growths, called Intestinal caeca, that run
upto 22nd or 23rd segments. These caeca arevascular & providedinternally with minute ville.
b)Typhlosolar Region:-This part lies between 27th segment upto 23-25 segments infront of anus. This part
is provided with large median, glandular, vascular, dorsal, longitudinal fold interndlly, called a Typhlosole. It hangs in
the dorsal wall like a curtain, in lengthwise manner. Paired Lymph Glands occur in each segment.
c)Post Typhlosolar Region(Rectum):-It includes the last 23-25 segments & open out through Anus at
segment. It has no typhlosole.
Food, Feeding & Digestion
Food:- Earthworms feed upon dead organic vegetations (humus) present in the scarcity of humus, it
also can feed upon the minute, tender parts of vegetations.
Feeding:- Earthworm feeds (Ingosts) its food by pumping or sucking action of its pharynax. It presses
its mouth against soil & contraction of pharyngeal wall draws the soil (humus) into the buccal chamber & to the pharynx.
Digestion:- No digestionof food occurs in buccal chamber when the food reaches the pharynx, it gets
mixed with salivary secretion of chromophil cells. This section consists of mucin that lubricate the food & an enzyme,
Proteolytic (protease) digests proteins. No digestion occurs in oesophagus. The gizzard acts as a grinding machine, that converts
the food into fine masses. This function is helped by the circular muscles & also the sand grains come with food. The
internal cuticle protects from injuiry. In stomach protine is digested by proteslytic enzyme chalky section of calciferous
glands neutralises the acidity of soil. Intestine is the main site of food digestion. The digestive juice of intestine contains
Pepsin digests proteins into peptones & proteases; Trypsin digests peptones & protease into amino acids; Amylase digest
starch into maltose; Lipase digests fat into fatty acids & Glycoses, Cellulase digests cellulose into celluobiose. Digested
food is absorbed mainly in typhlosolar part of intestine. The digestine area is increased by typhlosole. The secretion of
lymphs glands acts an antiseptic & antibiotic agent to kill germs & bactria in the food. Undigested food & soil
are stored in the Rectum & eliminated to outside in the form of worm castings. The castings of Earthworm are distinct,
small & round balls or peuets.
In Earthworm (pheretima posthuma), the excretory system is well developed & elaborated. The excretory system is performed
by segmentally arranged, microscopic, coiled, glandular & vascular & complicated excretory tubes, called as Nephridia.
The Nephridia are found in all segment of the body of earthworm except the first 2 or 3 segment. According to the position
& structure of Nephridia in the body, 3 types of Nephridia are found: -
(1) Septal Nephridia, (2) Pharyngeal Nephridia, (3) Integumentary Nephridia
1) SEPTAL NEPHRIDIA
These are the largest & well-developed Nephridia among the 3 types, so they are also called typical nephrida. These
Nephridia are attached to the both faces of each septum, behind 15th segment to the last segment. There are 40 to 50 Nephridia
on each side of the last septum, so each coelomic compartment (segment) has 80 to 100 septal Nephridia. A septal Nephridium
consists of following parts.
(i) Nephridiostome - It is expanded, rounded & funnel-shaped terminal part of the Nephridium, which opens into
the body cavity (coelom). It has a median pore, called ostium, which is guarded by upper & lower lips & their margins
are provided by cilia. The Nephridiostome is continued at its back by a short, narrow, ciliated & bent-tube, called Neck
that joins the Nephridiostome with the main body.
(Ii) MAIN BODY- It is a coiled & main part of septal nerphridum & it can be divided into - a short, flattened
& uncoiled straight -tube & a long, spirally-coiled Twisted loop, that joins the Terminal duct.
The straight lobe is rounded & free at its distal end but opens into the twisted loop at its outer end. The Twisted
loop can be distinguished into a proximal limb & a distal limb, which remain spirally, twisted (coiled) upon each other.
The distal limb is the direct continuation of straight lobe. The proximal limb opens into the terminal duct. The free-coiled
part of twisted rope bends to an angel to one side & is called as apical lobe. The total coils proximal & distal limbs
are one special Nephridium is 9 to 13 in number.
(iii) Terminal Duct - It is a short wide tube & is the posterior continuation of proximal limbs of twisted loop.
It attaches the Septal Nephridium to Septal Excretory Duct.
(iv) Nephridial Tubules - The glandular mass of each septal nephridium is crossed by parallel, branched & ciliated
tubules called as Nephridial tubules or ciliated tracts tubules. The matters collected are passed out through these tubules.
The numbers of these
Tubes are 4 in straight lobe 3 in basal & 2 in apical part of twisted loop & only a single tubule in the Neck &
Terminal duct.
All the Terminal ducts of each side of coelom open into a pair of Septal Excretory Ducts, that runs transversely along
the septum of each segment. In turn, the septal excretory ducts open into a pair of Supra-Intestinal Excretory Ducts, which
are thick-paired ducts that lie & run on the dorsal side of intestine & extend longitudinally from 15th to the last
segments. These Supra-Intestinal Excretory ducts are connected to the intestine in each segment by small & narrow tubules
on dorsal side.
The waste excretory matters from the coelomic-fluid are collected by ciliary-motion of Nephridiostome & pass out in
the following route.
Nephridiostome Main Body Terminal Duct Septal excretory Duct
Outside Anus Intestine Supra Intestinal Excretory duct
The excretory matters collected by septal Nephridium consists of 50% Urea, 42% Ammonia, 0.6% Amino acids & 7.4% other
compounds. (Refer the figure)
2) Pharyngeal Nephridia
These are 3-paired tufts (bunches) of Nephridia found on either side of pharynx & oesophagus in 4th, 5th & 6th
segments. Each tuft consists of hundreds of small, coiled Nephridia, similar to septal Nephridia but are smaller & without
Nephridiostome. Each tuft is covered with blood glands. All the Terminal ducts of the nephridia in each tuft join together
to form a thick walled common Excretory Duct. The paired common excretory Ducts of the tufts of 6th segment run up & open
into the buccal chamber & those of the tufts of 4th & 5th segments open into the pharynx but crossing each other.
These Nephridia extract the unwanted excretory matters from the respective segments & also from blood-glands by diffusion
process.
3) Integumentary Nepheridia
These are the minute, smallest & V-shaped Nephridia without Nephridiostome. They are attached inside the lining of
body wall from 3rd to the last segment. The Terminal duct of each Nephridium opens on the surface of body wall through Nephridiospores.
There are 200 to 250 integumentary nephridia in each segment but in the clitellum (14th, 15th & 16th segments) their number
is 10 times more than normal (i.e. 2000-2500) so constitutes forests of Nephridia. Integumentary nephridia extract the nitrogenous
waste matters from the body wall by diffusion process & pour out directly through Nephridios pores.
Out of the 3 types of Nephridia, the Septal Nephridia & Pharyngeal Nephridia pour out their collected excretory matters
passing through Alimentary canal, so they are called as Endonephric Nephridia, where as the Integumentary Nephridia pour out
the collected excretory matters directly outside, so they are called as Exonephric Nephridia.
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Nervous System
The nervous system is well developed & concentrated. If consists of 3 parts - central, peripheral
& sympathetic nervous systems.
1) Central Nervous System
A pair of closely united, white & pear-shaped cerebral ganglia (brain) lies dorsally in
the 3rd segment in the grove between buccal-chamber & pharynx. A pair of thick shout circum (peri) pharyngeal connectives
arises from the lateral sides of cerebral ganglia, which encircle the pharynx & meet ventrally in a pair of fused sub-pharyngeal
ganglia that lie beneath the pharynx in the 4th segment. In this way, a complete nerve ring (never-collar) is formed around
the pharynx. From the sub-pharyngeal ganglia, the ventral line to the posterior end of the body. In each segment, the ventral
nerve cordsloght enlarges to form the segmental ganglia.
Itistologically, the nerve-cord consists of never fibers & nerve cells. The nerve fibers
from the core of nerve cord. There are two such cores in the nerve-cord so it is double in nature. On the ventral side of
cores & on the sides there are nerve- cells. The nerve cells are of 2- types the more nervous & association neurons.
These 2-cores & nerve-cells (entire nerve-cord) in externally covered by peritponerve (perinorium) below which is a larger
of fibrous sheath called Epineuria. In between there two there is longitudinal muscle fibers. In the region of the segmental
ganglia, the two cores of nerve fibers are completely fused along the middle line.
In the mid-dorsal region of the nerve cord. There are 4-Giant- fibers (nevrocords) a median,
a sub median & two lateral giant fibers. There giant fibers run through the entire length of the nerve cord.
2) Peripheral Nervous System
Each lobe of cerebral ganglia gives-off 8 to 10 nerves which supply the branches to the prostomium
& buccal-chamber. Pairs nerve front per pharyngeal connectives supply the peristomium & buccal chamber. Paired nerve
from sub-pharyngeal ganglia supply the structure in the 2nd, 3rd & 4th segments. Each segmental ganglia of ventral nerve-cord
gives off 3-pairs of lateral nerves (one-pair in front & 2-pairs behind) not supply the body wall, wall of Alimentary
canal & internal organs of the respective segments.
3) Sympathetic Nervous System
It consists of extensive nerve plexus that are connected with circum pharyngeal connectives
& spread beneath the epidermis, within muscles of body wall & on alimentary canal.
Working of Nervous System
The Nervous system controls & co-ordinates all the activities. The nerves are mixed type,
consisting of both afferent (sensory) & efferent (motor) fibers. The afferent start from a sensory (receptor). The organ
or cell of epidermis & terminate in ventral nerve cord. The sensory impulses (stimuli) are from the receptors by the afferent
fibers to the ventral nerve cord, from where they are reflected back as motor impulses along the efferent fibers to the muscles,
which contract.
Often an Adjustor neuron may be present between the afferent & efferent neurons through
which an impulse may be conveyed to the opposite sides of the same or other segments, thus bringing about the co-ordination
of the body activities.
Giant fibers of the nerve cord conduct nerve impulses much more rapidly than the ordinary nerve
fibers & cause sudden movements of the entire body when a part of the body is stimulated. The rate of conduction in the
giant fibres is about 1.5 meters in one second while in the ordinary fibres it is about 25mm in one second.
Reproductive System
Earthworm reproduces only by sexual method. It is Bisexual with well-developed & complicated male & female reproductive
organs concentrated to some of the anterior segments. In spite of being bisexual, no self - fertilization occurs but only
cross-fertilization occurs. It is because of the positions of male & female organs in different segments & due to
portentous condition, i.e. sperms mature earlier than ova.
Male Reproductive Organs
1) Testes: -These is the main organs for sperm formation. There are 2 pairs of minute, white organs & lobed Testes,
found one pair in each of 10th & 11th segments. They are located below the alimentary canal, on either side of nerue cord
& attached to the anterior inner surface of each testis. Each tests is made up of 4-8 digited processes, contdining spermatogonia.2)
Testes Sacs: -each pair of testes is enclosed by a pair of sacs that lie in 10th & 11th segments. Besides Testes, the
testes sacs also enclose spermeducal funnel. A pair of seminal vesicle present in posterior testes sac.3) Spermeducal Funnel:
-These is 2 pair of expanded structures with ciliated margin & a pore in the center. They are behind each testis, in the
same segment & enclosed within the same testes sac in 10th & 11th segments.4) Seminal Vesicles: -These is 2 pairs
of whitish hollow structures lying in 11th segments. The anterior pair of seminal vesicles is within the posterior testes
sac & those of posterior pair lie freely in 12th segment. Each of the seminal vesicles communicates to the anterior testes
sacs by short ducts.5) Vasa Deferential: -Each spermeducal funnel leads behind into a slender, ciliated & thread like
vasa deferential to each other posterior along the ventral body wall up to 18th segment to join with prostatic duct.6) Prostate
Glands: -These is a pair of whitish, flat, solid, irregular & lobulated masses, located in the 16-17 to 20-21st. segments.
The glandular parts of the glands secrete prostatic fluid. On each side the duct of prostate gland & 2 ducts of vasa deferential
join to form a common prostatic & spermatic duct. The two common prostatic & spermatic ducts open on the ventral body
wall through male genital apertures, on the ventral body wall through male genital apertures, on each side on 18th segment.
7) Accessory Glands: - These are 2 pairs of circular glands, each pair found in 17th & 19th segments. They open outside
on 2 pairs of genital papillae, on the ventral surface of 17th & 19th segments.
Female Reproductive Organs
1) Ovaries: -A pair of small, white & digested ovaries is attached to the header face of 12/13 septums, hanging in
the 13th segment, on eon either side of nerve cord. Each ovary is a compact mass made up of finger like processes, in which
ova are arranged linearly, in the order of development.2) Oviducal funnels: -These is a pair of saucer shaped structures with
much folded & ciliated margin & a central pore. They lie just behind into the oviduct.3) Oviducts: -Each of the oviducal
funnels run backwards in the form of short, conical & ciliated oviducts, on either side, bore the septum 13/14 & converge
to meet in the body wall beneath the nerve-cord, forming a short common oviduct that opens outside through a female genital
aperture, lie mid ventrally on 14th segment.4) Spermathecae: -These are 4 pairs of flask-shaped bodies, one pair situated
in each of 6th, 7th, 8th & 9th segments. The sperms are stored & nourished in the spermathecae after copulation. The
spermathecae open outside through 4 pairs of spermathecal pores, lying intersagmentally between 5/6, 6/7, 7/8, & 8/9 segments
ventrally.
Copulation
The sperms of one earthworm are transferred to another during copulation. This process generally takes place at night,
during rainy season & lasts for about one hour. The two worms apply to each other by their ventral our faces with head
end, pointing to against a pair of spermathecal pores of other. The pore raised into a small duct that is inserted into the
spermathecal pore of another worm & sperms are discharged into the spermathecae. Slight movement fills all the 4 pairs
of spermathecae filled with sperms in both. After the copulation, the worms separate & go to reside or shady & moist
ground & ready for cocoon formation.
Cocoon formation
After copulation, the gland - cells of the clitella become active & begins to secrete a viscid & gelatinous fluid,
which hardens gradually on exposure to the air & forms a tough but elastic tube, which becomes a membranous tube (cocoon)
around the clitellum. The epidermal mucus cells around the clitellum into the cocoon also secrete a slime tube. As the worm
begins to wriggle behind, the slime tube (cocoon) is slipped forward, toward the head. As it passes over the female genital
aperture, it receives ova at 14th segment & as it passes to the anterior segments, it receives sperms from spermathecae,
which were received & stored during copulation. As soon as the worm has entirely with dreous it, the elastic ends of cocoon
close & it becomes a small spherical cocoon. Lay on the ground. Inside a sperm fertilizes the cocoon one ovum & only
one zygote begin to develop & nest degenerate, cocoon provides nourishm to the embryo. After histogenesis, the embryo
develops into a young Earthworm.
Blood Vascular(circulatory) System
The blood vascular (circulatory) system is concerned for the transport of nutrients, oxygen, and carbon
dioxide. Nitrogenous, waste products, Enzymes etc. Inside the body to their respective parts. This system is more complex
& well developed in Earthworm. It is of closed type & includes blood, blood vessels, blood capillaries & blood
glands. Blood is bright red coloured due to the hemoglobin dissolved in plasma. Nucleated corpuscles (Leucocytes) hemoglobin
dissolved in the plasma but without Erythrocytes (RBC). The blood always flows in blood vessels in a definite circuit.
The arrangement of well developed longitudinal & being different in the first 13th segments from
that in the rest of the body. So this system is differentiated & studied under two headings.
1) Circulatory System in the Anterior (first 13th) Segments.
In the anterior region of first up to 13th segments of Earthworm, there are 4 types of longitudinal
blood vessels, which are being connected by transverse vessels. These blood vessels are described as below.I) Dorsal Blood
Vessel: -It is the longest & most prominent longitudinal blood vessel that runs mid dorsally above the alimentary canal
& extends through out the body length. Its walls are thick, muscular & contractile. It is provided with a pair of
internal values in each segment, which allow only forward flow of blood.
From anterior to the 13th segment, this blood vessel is mainly a distributing vessel. This vessel extends
interiorly up to the 2nd segment & supplies blood in 2nd, 3rd, 4th, 5th, 6th & 8th segments by pulsatile branches
(capillaries) to respective parts of anterior alimentary canal & other organs.
The blood from dorsal vessel is transports to the ventral blood vessel by 4 pairs of muscular, valvulor
& pilsatile Hearts. The anterior 2 pairs of hearts lie in the 7th & 9thsegments are known as the same segments. The
posterior 2 pairs of hearts lie in 12th & 13th segments, are known as lateral oesophageal Hearts. They connect & carry
blood from dorsal vessel as well as from supra oesophageal vessel to the ventral blood vessel.ii) Ventral Blood Vessel: -This
vessel is situated in the mid-ventral line below the alimentary canal & runs through the body length. This vessel is thin
walled & is without internal values. Blood always flows in backward direction & this blood vessel is chief distributing
vessel.
Up to the first 13th segments, this vessel gives off a pair of ventro tegumentary vessels in each segment,
which supply blood to body-to-body wall, nephridia, reproductive organs etc. In 7th & 9th segments, this vessel receives
blood from dorsal blood vessel through lateral hearts & in 12th & 13th segments it receives blood from dorsal blood
vessel & supra oesophageal vessel the lateral oesophageal hearts.iii) Lateral Oesophagel Blood Vessels: -The lateral oesophagel
blood vessels are a pair of longitudinal vessels that run ventrolaterally to the alimentary canal from anterior to 13th segment.
They run freely but parallel to anterior alimentary canal, but from 9th to 13th segments, they are attached to the outer wall
of stomach. These blood vessels are thin-walled, non contractile & without internal valves. Blood flows from anterior
to posterior direction.
These paired blood vessels are chiefly collecting blood vessels. They collect blood from the body,
wall, septa, gut, nephridia, reproductive organs etc. by fine branches (capillaries). In the 10th & 11th segments, these
vessels are connected to the supra oesophageal vessel by 2 pairs of non muscular, non valvular, non contractile & thin
walls chambers, called as Anterior loops, thus, blood flows from lateral oesophageal vessels to supra oesophageal vessels
through Anterior loops 10th & 11th segments.iv) Supra Oesophageal Blood Vessel: -It's a single & shortest longitudinal
blood vessel that lies closely attached to dorsal wall of stomach above, from 9th to 13th segments. It's thin walled, non-contractile
& non-vavular vessel, which functions as collecting & distributing blood vessel. It collects blood from lateral oesophgeal
vessel through. Anterior loops in 10th & 11th segments & supplies blood to ventral vessel through lateral oesophageal
hearts in 12th & 13th segments.
2) Circulatory System in the Posterior (intestinal region or behind 13th to last) Segments.
In the posterior segments (intestinal region) behind 13th to the last segment of Earthworm, there are
three main longitudinal blood vessels, which are connected by transverse vessel. These three longitudinal blood vessels &
their associated vessels are as follows.i) Dorsal Blood Vessel: -It is the largest, longest, most distinct longitudinal blood
vessel that runs mid-dorsally above the alimentary canal from anterior to posterior end of the body. It is thick walled, contractile
& muscular vessel, with a pair of valves in each segment that allow the blood to flow forward direction from backward
only.
In this posterior segments (Intestinal region), behind 13th to last segment, the dorsal blood vessel
is the main collecting blood vessel. It is receives blood in each segment by a pair of commissural vessels & two pairs
of dorso intestinal vessels.
The commissural vessels form a loop behind each septum, around the intestine, connecting the dorsal
blood vessel with the sub neural vessel. This vessel on its way to dorsal blood vessel, receive, blood from nephridia, body
wall, reproductive organs etc. On each side of septum & along with the blood from sub neural vessel, pours to the dorsal
blood vessel. Septum of eboanches of commissural vessel in the vessel that supply blood to the instants forms a septo intestinal.
The dorso intestinal vessels collect blood from two pairs of transverse & typhlosolar vessels, from outer & inner
side of the intestine.ii) Ventral Blood Vessel: -This longitudinal vessel is situated in the mid ventral line of the body,
below the alimentary canal & extends through but the length of the body. It is thin walled & without internal valves.
The flow of blood is from anterior to posterior part of the body.
In these posterior segments, behind 13th segments of the body, this vessel function as a distributing
vessel, it supplies blood to the respective organs & parts in the segments.
In each segment, the ventral blood vessel gives out a pair of ventro tegumentary vessel, one on each
side, in front of each septum. This vessel gives blood to the body wall, nephridia, Gonads etc.
The ventral blood vessel also gives out a ventro intestinal vessel in each segment, which supplies
blood to the lower part of intestine.iii) Sub Neural Blood Vessel: - It is a single median longitudinal blood, which is formed
by the combination of two lateral oesophageal Blood vessels of anterior segments. This blood vessel runs mid ventrally, below
the ventral nerve cord, from 14th to the last segment. This sub neural vessel is thin walled non-valvular vessel & functions
for collection & distribution of blood. Blood flows in this vessel from anterior to posterior direction.
This blood vessel collects blood from body wall & respective organs of the body in the segments
by small delicate branches. It gives its blood to the intestine & some blood from this sub neural blood vessel goes to
the dorsal blood vessel through the com missural vessel in each segment.
Sachit
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