190 ARTHROPOD A 



quite active in the evening, and if you visit a car in which 

 they are kept, at this time of the day, you are likely to find 

 them crawling up the sides, falling over and swimming on 

 their backs. In this position it is easy to determine how 

 they swim. The animals are very hardy and will stand even 

 complete removal from the water for days at a time. During 

 the spring and early summer, eggs are deposited in the sand; 

 the male holding to the edge of the abdomen of the female 

 with claws modified for the purpose, is dragged after her. 

 If possible, the method of egg deposition and fertilization 

 should be observed. 



1. The animal consists of a hoof-shaped cephalothorax, 

 an abdomen, and a caudal spine. How are these joined? Is 

 there any indication of segmentation of any of them? 



2. Examine the eyes with a lens and see that they are 



compound. 



3. On the lower side of the cephalothorax notice the ap- 

 pendages. Are they all built on the same plan? Compare 

 them in male and female. Do you know what the modifica- 

 tions are for? Compare the pincers with those of a lobster. 

 The first pair of appendages is called the chelicerae. Be- 

 tween the bases of the last pair of walking legs are the 

 chilaria. Behind the chilaria is the broad flat operculum. 

 Does this show evidence of being modified appendages? 

 What is its function? 



4. Between the bases of the cephalothoracic appendages 

 is the mouth. Do the bases of the appendages show any 

 modifications that may serve as teeth? Can the pincer- 

 bearing appendages be so bent as to be used in feeding? 



5. Along the sides of the abdomen notice the movable 

 spines. How many are there? 



6. Under the operculum are the gills. How many groups 

 are there? Are they arranged in pairs? How are they at- 

 tached to the body? Are they movable? What reason is 

 there for moving them? Examine a bunch of gills, frequently 

 called a gill book, and see how it is formed. 



