76 Elementary Manual of Zoology. 
(5) The mouth, which js the anterior opening of the digestive 
tract. It is situated at the front end of the body. 
(6) The anus, or posterior opening of the digestive tract, 
which is situated at the end of the last segment. 
(7) The genital openings, which lie on the ventral surface. 
The students will best be able to make them out when 
they have dissected the organs with which they are 
connected. 
(8) The mid-dorsal pores, which are minute holes that serve to 
place the body cavity in communication with the ex- 
terior, They lie between the seements in the mid-dorsal 
line. 3 
Stretch the anterior segments of the worm a little, by gently pull- 
ing the animal through the fingers. 
Pin the animal, ventral surface downwards, on to the weighted 
bark. Two pins will be sufficient. One of them should be inserted 
through the lip and the other as far back as possible. Now with 
scissors make a longitudinal slit in the dorsal wall of the integument. ” 
Work from behind forwards, and take great care not to cut through 
more than the outer layer. Dissect back the flap on either side, cutting 
through the numerous little membranous partitions by which the 
digestive tract is attached to the outer wall. Pin back the flap on 
either side. The students will now have exposed the following or- 
gans :— ‘ 
(1) In the centre line a longitudinal vessel (dorsal vessel) which lies 
immediately above the digestive tract, and can at once be. 
recognised by the red colour of the blood it contains. 
(2) The digestive tract, which is a thick, soft, dark-coloured tube 
throughout the greater part of its length. 
(8) The blood-vessels, which pass round the ‘digestive tract and 
connect the dorsal vessel with the ventral vessel which 
lies below. 
(4) The reproductive organs, which lie on either side of the 
digestive tract. 
Now examine the digestive tract in detail and observe that it is a 
straight tube which extends from the mouth in front to the anus behind. 
Make out the following parts in it, examining from in front back- 
wards :— 
(1) The mouth, 
(2) The pharynx, with expanded muscular walls, 
(3) The esophagus, which connects the pharynx with the 
gizzard, 
