THE CRAYFISH. 29 



the metastoma. (The metastomata differ from the 

 maxillae in pointing outward and in being undivided.) 

 Remove it and complete the series of mouth parts, — 

 mandible, first maxilla, second maxilla, first max- 

 illiped, second maxilliped, third maxilliped. Remove 

 the corresponding appendages of the other side, lay 

 them in a row facing those of the opposite side, as 

 before removal, but not now overlapping each other, 

 and make a drawing of the series, naming them. 



12. The long projections in front of the head are the 

 antennae. Seize one of them with the forceps, and 

 pull about in all directions, to make out the large 

 segment, at its base, under the head. On this basal 

 segment find a small white cone, with a hole at its 

 summit. This is the aperture of the green gland, 

 in the head, which acts as a kidney in throwing off 

 certain waste products from the body. Remove the 

 antenna, with the whole of this big segment at its 

 base. What, probably, is the use of the blade-like 

 branch of the antenna just under the eye? Compare 

 the antenna and its branches with a swimmeret. 



13. Above the antennae are the antennulae. Remove 

 one of them and compare it with a swimmeret. 



14. In the base of each antennule, just underneath the 

 eye, is the ear-sac. 



15. With the forceps pull the eye about to see its range 

 of motion. Pull it out by its stalk, and examine with 

 lens and microscope its black tip, or cornea. Is it 

 simple or compound? 



After removing the cephalothoracic appendages, 

 and the carapace, carefully clean and thoroughly 

 examine the framework of the cephalothovax, still 



