Practical Course. 77 
(4) The gizzard. This is an expanded whitish organ, with thick 
muscular walls,in which the food is crushed before 
passing into the soft intestine. 
(5) The long straight intestine, with dark-coloured bulging walls. 
It extends throughout the rest of the body and connects 
the gizzard with the anus, 
Now examine with a lens the blood-vessels which pass round the 
digestive tract from the dorsal vessel. Notice that five of the vessels 
which encircle the intestine, inimediately behind the stomach, are much 
expanded. These have contractile walls and are sometimes called 
hearts. They serve to keep up the circulation of the blood, which 
courses up the dorsal vessel and down the ventral vessel. 
Now examine the reproductive organs. These vary a good deal in 
different species and at different times of the year, but the students 
will usually be able to make out the following parts :-— 
(1) A large pair of white globular sacs (receptacula seminis), in 
which the spermatozoa, received from another individual, 
are stored. hese sacs lie on either side of the esophagus 
and open by slits to the exterior below. : 
(In one common Calcutta species there are three of these sac-like 
recepticula, one behind another.) 
(2) A pair of large yellowish glandular organs (vesicule 
seminales), which contain the testes. These lie on either 
side of the intestine behind the stomach and close to the 
three hindmost pairs of hearts. 
(3) A pair of white tubes (vasa deferentia) which are sometimes 
much coiled ; the greater part of them lies some distance 
behind the vesicule seminales. They serve to convey 
the spermatozoa to the male genital openings, which lie 
on the ventral surface of the cingulum. 
The ovaries are smaller and more difficult to make out, and it is 
only exceptionally that the students will be ableto see them. They lie 
posteriorily to the vesiculz seminales, the eggs passing out by a pair 
of short tubes, which lie one opposite each ovary. 
The students should now make asketch of the dissection and mark 
in the names of the organs they have been able to recognise. 
Carefully dissect out the digestive tract, so as to expose the ventral 
blood-vessel, which runs down the body immediately below the digest- 
ive tract. Trace where the connecting vessels from the dorsal vessel 
join it, and notice the branches that run along the sides of the 
esophagus. Below the central vessel see the large white nerve 
(ventral nerve chain), swollen slightly in each segment, Trace it 
throughout the whole length of the animal, noticing the little nerves 
