48 STUDIES OF ANIMAL TYPES 



in forked stylets. Attached to each side of the first ab- 

 dominal segment of the females will often be found a sack 

 of eggs. 



Make a drawing showing all these points. 



B. CYPRIS. It is usually found with cyclops but differs 

 from most crustaceans in having a bivalved shell. It is 

 often mistaken for a mollusk. The shell is really composed 

 of the carapace, which is divided into two parts. The halves 

 are hinged along the dorsal edge like the valves of a clam. 

 Within the shell are seven distinct pairs of appendages 

 which betray the family connections of this little animal. 



C. DAPHNIA. Sometimes the aquarium is alive with 

 these grotesque, hump-backed crustaceans that travel with 

 a jerky motion like cyclops. The whole body is covered 

 with the carapace. The head is drawn down, and the back 

 is humped up like a stooping, round-shouldered man. The 

 antennae are long and are thrown out in front. Note the 

 five pairs of leaf like swimming feet. 



D. CRABS. If possible, get a rock crab for the collec- 

 tion. Compare it with the crayfish. Note the greatly 

 broadened carapace. Note the abdomen, which is curled 

 beneath the cephalothorax and is permanently carried 

 there. Compare the antenna? and the antennules with 

 those of the lobster. 



HERMIT CRAB. If one of these is in the collection, note 

 the soft abdomen. Why does this crab need a shell, and 

 the rock crab not? 



XVI. THE LOCUST, OR GRASSHOPPER 



Materials. Specimens of locusts alive and preserved, glass slides, 

 cover glasses, compound microscope, glass bell jar, dissecting pan, 

 pins, dissecting instruments, 



