64 
ZOOLOGICAL EXERCISES. 
large white spermatheca, rounded posteriorly, and 
passing into a narrow tube anteriorly. Just where 
the spermatheca gets narrow, the blue colouring of 
the convoluted tube ceases, and at this point the vas 
deferens separates from the oviduct and passes to the 
penis. Notice that the retractor muscle is attached 
to the middle of the penis. Notice also at the in- 
ternal extremity of the penis a short ceecal tube, 
with three to five small branches. This is the 
prostate gland. Examine microscopically the struc- 
ture of the parts. Probably the ovo-testis will be 
found to contain large numbers of spermatozoa, and 
afew ova. Notice that the ova lie near the margin 
of each follicle of the sex gland, while the sper- 
matozoa are developed in the interior. Cut across 
the oviduct and penis sac at their opening, and 
remove the whole of the reproductive system. Cut 
the retractor muscle of the head near its origin ; turn 
it back, and notice the branches it sends to the 
tentacles. Cut it out, and examine with the micro- 
scope. Notice that it is non-striated. 
7. Nervous system.—Examine the nerve collar in situ. 
It consists of two large cerebral ganglia, united 
superiorly by a broad transverse commissure. In- 
feriorly, the cerebral ganglia are united to a compli- 
cated mass of ganglia composed of two large white 
pedal ganglia, above which is a transverse row of 
six small ganglia forming the parieto—splanchnic 
system. With a curved needle trace the nerves from 
the cerebral ganglia to the eyes and tentacles; and 
also the numerous cords given off posteriorly by the 
infra-cesophageal ganglionic mass. Extract the whole 
collar, put it on a slide in water, spread it with a 
