158 AKTHBOPODA. 



ARACHNOIDEA: 



LIMULUS. (Horseshoe Crab.) 



Notice the way in which the animal crawls upon the bottom. 

 Is it well protected from enemies? Examine it carefully for 

 parasites and for animals that are attached to it. Disturb it 

 and see if it will swim. The animals are usually 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 posi- 

 tion 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 com- 

 pound. - \ & 6tt v ? 



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

 dages. Are they all built on the same plan? Compare them in 

 male and female. Do you know what the modifications are 

 for? Compare the pincers with those of a lobster. The first 

 pair of appendages is called the chelicerce. Between the bases 

 of the last pair of walking legs are the chilaria. Behind the 

 chilaria is the 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 modifi- 

 cations that may serve as teeth? Can the pincer-bearing ap- 

 pendages 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 



