Practical Course. 81 
around the gullet to join the ganglia, which lie on the ventral floor of 
the body. 
Now unpin the animal], turn it over and examine the appendages, 
pulling them off one by one with forceps, beginning from behind, and 
sketch them in order in a note-book. The appendages are as follows, 
working from behind forwards :— 
(1) Attached to the abdomen :— 
(2) In the female, four pairs of bifureated swimming 
appendages, 
(2), In the male, two pairs of small pointed appendages. 
(2) Attached to the cephalothorax :— 
(a) Four pairs of large jointed legs on which the 
animal walks, . 
(2) One pair of large jointed pincers (chele). The 
pincers are formed by the last joint, which works 
against a prominence on the last joint but one, 
(ec) Three pairs of jointed appendages (maxillipedes), 
the most posterior of which forms 4 pair of broad 
plates which cover up the mouth. 
(d) Two pairs of little white appendages (mazille), the 
posterior pair of which are modified into oval 
plates (seaphognathites), which serve to pump the 
water out of the branchial chamber. 
(e) One pair of hard jaws (mandibles), each with a little 
jointed appendage (palp). 
(f) One pair of movable stalked eyes. 
(9) Two pairs of minute jointed antenne. 
Notice that the little swimming appendages, attached to the abdo- 
men of the female present the same essential structure as all other 
appendages. 
Notice the little auditory organs at the base of the front pair of 
antenne. 
DISSECTION OF THE COCK ROACH. 
“The best cockroaches for dissection belong to the species Perzplaneta 
americana, Deg. This is a large form which is scarce in Debra Dun, but 
easily procurable in Calcutta. A large number should be procured. 
They should be preserved in alcohol until wanted for dissection, The 
fresher they are the better. In Calcutta they are known as tilchatta. 
Amongst the specimens ‘procured for dissection there are pretty 
> certain to be some immature ones (larve), Notice that they are 
wingless, but otherwise very much like the full-grown individuals. 
a 
