DISSECTION OF HIRUDINARIA GRANULOSA (LEECH)

DISSECTION OF HIRUDINARIA GRANULOSA (LEECH)

It is the common cattle leech. For studying external features, take freshly killed specimens with chloroform vapours.

External features of Hirudinaria Granulosa (Leech)

1. Number of segments : 33.
2. Number of annuli in a typical middle segment is 5.
3. Total length : 5 to 10 cm.
4. Parapodia and setae : Completely absent.
5. Shape: Body is dorso-ventrally flattened. It looks like ribbon-shaped when elongated and cylindrical when contracted.
6. Colour: The body is greenish brown and paler below than above. The dorsal surface is characterised by having yellowish, longitudinal bands spotted with black pigments, while ventral surface is irregularly mottled.
7. External annulation : Although the true segments are 33 only, but each segment is further divided, into generally 5 superficial rings or annuli.
8. Divisions of the body : Body is divided into the following regions :
   • Cephalic region or head region: It comprises of first 5 anterior segments and includes anterior sucker, mouth, jaws and eyes.
   • Pre-elitellar region : It is formed by 3 complete metameres (6th, 7th and 8th).
   • Clitellar region : It is also made up of 3 segments (9th, 10th and 11th).
   • Middle region : It is composed of 11 segments from 12th to 22nd segments.
   • Caudal region : It is made of 23rd, 24th, 25th and 26th and somites or segments.
   • Posterior region : It contains 26 to 33rd segments.
9. Suckers: Each end of the body contains suckers namely anterior and posterior suckers.
10. Apertures :
    • Nephridiopores : 17 pairs. One pair is found on the last annulus of each of the 6-22 segments.
    • Male genital opening : Found on the midventral line of the annular groove between the 2nd and 3rd annuli of the 10th somite.
    • Female genital opening: Lies mid-ventrally between the second and third annuali of the 11th segments.
    • Anus : Lies mid-dorsally on the 26th segment at the base of the posterior sucker.

General anatomy of Hirudinaria Granulosa (Leech)

Procedure :- Leaches are killed by chloroform or they may be (narcotised) in water by adding few crystals of magnesium sulphate or menthol. The wellfed leeches have swollen appearance, because crop is filled with blood. It is necessary to extract blood by pressing the body between thumb and first finger. The blood, in this way, comes out from the mouth. Stretch the leech and pin it on both the suckers to the dissecting dish with dorsal side upwards. Make a mid-longitudinal incision through the skin from anterior end.

Care must be taken not to cut the alimentary canal. Remove carefully the connective tissue and botryoidal tissue between body wall and digestive tube. Pin the flaps on the sides. Study the following parts ”

• Alimentary canal of Hirudinaria Granulosa (Leech) : See details in alimentary canal dissection.
• Circulatory system of Hirudinaria Granulosa (Leech) : It consists of 4 longitudinal haemocoelomic channels, which are reduced coelom, namely (i) dorsal haemocoelomic sinus, (ii) ventral haemocoelomic sinus, and (iii) 2 lateral haemocoelomic sinuses and their branches.
• Excretory system of Hirudinaria Granulosa (Leech) : 17 pairs of nephridia. First 6 pairs are pre-testicular lying in the 6 to 11 segments. These are devoid of testis sacs. Last eleven pairs are testicular lying in the 12 to 22 segments. Each nephridium is composed of twisted glandular main lobe, spherical muscular bladder, nephridiopore and nephrostome.
• Nervous system of Hirudinaria Granulosa (Leech): For details refer to dissection of nervous system.
• Reproductive system of Hirudinaria Granulosa (Leech) : Leech is hermaphroditic. Male and female sex organs are found in the same animal. For details see dissection of reproductive system.

Alimentary canal of Hirudinaria Granulosa (Leech)

It consists of the following parts

1. Pre-oral chamber : The concavity of the anterior sucker is called as pre-oral chamber containing mouth at its base.
2. Buccal cavity : Mouth leads into buccal cavity having 3 serrated chitinous jaws, which mark a tri-radiate wound on the body of the host.
3. Pharynx: Extends from the 5th to 7th segment. It is highly muscular and encircled by salivary glands.
4. Oesophagus: Very short and leads into crop.
5. Crop: Extends from the 9th to 18th segment. It consists of 10 crop chambers and each chamber has a pair of crop diverticula. The last diverticula are the largest and extend upto the 22nd segment.
6. Stomach: It lies in the 19th segment.
7. Intestine : Extends from the 20th to 22nd segment.
8. Rectum: Extends from the 22nd to 26th segment.

Reproductive system of Hirudinaria Granulosa (Leech)

Procedure: Leech is hermaphrodite. For details see dissection of reproductive system proceed as in case of general anatomy or alimentary canal. A. Male reproductive system It is associated with excretory organs from 12 to 22 segments and consists of the following parts :

• Testes sacs : 11 pairs, one pair each in segments 12th to 22nd. Each testis sac is very distinct, whitish and rounded structure.
• Vasa efferentia: From posterior border of each testis sac arises a minute sperm ductule called as vas efferens, which joins with the sperm duct of its side.
• Vasa deferentia: There are 2 longitudinal sperm ducts, running from 22nd to 11th segment on either side of the nerve cord.
• Epididymes: Each sperm duct ends in a convoluted mass called as epididymis in the 10th segment.
• Ejaculatory ducts It arises from anterior end of each epididymis and opens into atrium.
• Atrium: It is a pyriform sac, found between 9th and 10th segments. It has anteriorly placed prostate gland backwardly directed penis sac. B. Female reproductive system It consists of the following parts
  • Ovisacs: A pair of rounded sacs, found in the 11th segment.
  • Oviducts : Each ovisac gives a slender, short tube called as oviduct. The two oviducts form a common oviduct in the 11th segment.
  • Vagina: It is an elongated sac-like structure in the 11th segment. Note the presence of albumen glands anterior to vagina.

Nervous system of Hirudinaria Granulosa (Leech)

It consist of the following parts

1. Supra-pharyngeal or cerebral ganglia: Found above the pharynx.
2. Peripharyngeal connectives : They arise from cerebral ganglia and make a ring of stout nerves around pharynx.
3. Sub-pharyngeal ganglion : The connectives join a sub-pharyngeal ganglion.
4. Double-ventral nerve cord: It arises from sub-pharyngeal ganglion and runs in successive segments within ventral haemocoelomic sinus from the 6th to 26th segment.