CRUSTACEANS 



55 



!^^-. 



to swimmerets ? Do they likewise have the Y-shaped 



structure ? (Fig. 86.) 



If the swimmerets on the first abdominal segment are 



large, the specimen is a male. If they are small, it is a 



female. Which sex is shown in Fig. 82 ? 



Fig. 86 ? 



Carapace. — The covering of the head 



chest (cephalothorax) is called the cara- 

 pace. Has it free edges ? The gills are 



on the sides of the body and are covered 



by the carapace (Fig. 87). The projection 



in front is called the rostrum, meaning beak. 



Does the rostrum project beyond the eyes ? 



There is a transverse groove across the cara- 

 pace which may 

 be said to divide 

 the head from the 

 abdomen. Where 

 does this groove end at the sides ? 

 Legs. — How many legs has the 

 crayfish? How many are provided 

 with large claws ? Small claws ? 

 Is the outer claw hinged in each 

 of the large grasping pincers ? 

 The inner claw ? 



Appendages for Taking Food. — 

 If possible to watch a living cray- 

 fish eating, notice whether it places 



the food directly into the mouth with the large claws. Bend 



the large claws under and see if they will reach the mouth. 

 Attached just in front of the legs the crayfish has three 



pairs of finger-like appendages, called foot jaws(maxilli- 



peds), with which it passes the food from the large pincers 



FlG. 85. — 1, mandi- 

 ble; 2,3, maxillae; 

 4, 5, 6, maxillipeds. 



Fig. 86. — Crayfish 

 (ventral surface). 



