148 ARTHROPODA. 



esophageal connectives around the gullet (they anastomose just 

 behind it) to the cerebral ganglia. Along with the distribution 

 of the ophthalmic and antennary arteries, trace the nerves from 

 the cerebral ganglia to the eyes, antennse, antennules, etc. Why 

 should the nervous system be more concentrated than it is in the 

 lobster? . 



Make a drawing of the nervous system. 



Brooks: Hand-book of Invertebrate Zoology. 



Gurney: Metamorphosis of Corystes. Quart. Jour. Micro. Sci., 46, 1902:' 



EUPAGURUS. (Hermit Crab.) 



Examine a living specimen and see how it moves, and how 

 the aperture of the shell is closed by the two large claws when 

 the animal withdraws. 



With a hammer crack the shell away from the animal and 

 examine the twisted abdomen. 



1. Has it lost its symmetry in appendages as well as in shape? 



2. How many of the appendages have been retained ? What 

 is the function of these appendages? 



3. Remove several other specimens from their shells and 

 place them in a dish of sea-water together? Do they seem to 

 understand that they are not protected? 



4. Place an empty shell in the dish and see what happens. 



5. Put more empty shells in the dish, but be sure they are 

 not quite large enough for the crabs. Then add some larger 

 shells and watch the crabs test them to see which will serve 

 best. 



A drawing is desirable. 



Thompson: The Metamorphoses of the Hermit Crab. Proc. Bost. Soc. Nat. 

 Hist., 31, 1903. 



HIPPA. (Sand Mole.) 



On sand beaches, between low- and high-water mark, there 

 may frequently be seen the shallow depressions that mark the 

 places where these animals have burrowed. They may be dug 

 out with a shovel, but they quickly disappear again. 



