CRAYFISH OR LOBSTER. 69 



In front of the maxillipeds come two pairs of accessory 

 jaws (maxilhe). Remove them carefully and draw. Look 

 on the hinder maxilla for a large expansion, the gill- 

 bailer (scaphognathite) . Removing these parts exposes the 

 mouth, on either side of which is a strong jaw (mandible). 

 How do these jaws move in comparison with those of man? 

 Take one out and see of how many joints it is composed. 

 Draw. 



The cephalothorax is covered above by a large continu- 

 ous plate, the carapax. Does this show signs of somites? 

 With the forceps lift the hinder corner of the carapax on 

 the side where the mouth-parts still remain and see 

 where it joins the body. Then with the scissors cut away 

 the free portion, thus laying open the gill-chamber and 

 exposing the body-wall and the numerous gills or branchial. 

 Are any of these attached to the legs or to the body- 

 wall? Move the maxillae and see the operation of the 

 gill-bailer. Can water obtain free access to the gills? 

 Would the action of the gill-bailer tend to draw water 

 over the gills? Remove the gills one by one, noting 

 how many there are on each appendage (podobranckice) ; 

 on the joint uniting the appendage to the body (arthro- 

 branchice) and on the side of the body above each append- 

 age (pleurobranchice) . 



In front of the mouth occur the 'feelers/ or antenna?. 

 Could these be compared to the legs? Can you find 

 exopod or endopod in them? Examine the basal joint 

 of the larger or posterior one (the antenna proper), and 

 find an opening, the outlet of the green gland (see below r ). 

 Is it in any way comparable in position to the reproduc- 

 tive opening? In the smaller feelers (antennulse) look 

 for the ear-sac on the upper surface of the basal joint. 

 (It is covered with a thin membrane, around which hairs 



