CALLINECTES, PAGURUS 179 



antenna. It consists of a thin bladder, and, anterior to this, 

 a mass composed of a coiled tube which opens at the base of 

 the second antenna. 



Nervous System. — Find the ring of ganglia around the 

 ventral end of the sternal artery. 1 Trace the nerves from 

 this to the appendages and to the small abdomen. Trace the 

 circumesophageal connectives around the gullet (they an- 

 astomose 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, an- 

 tennae, etc. Why should the nervous system be more con- 

 centrated than it is in the lobster? 



Make a drawing of the nervous system. 



Brooks: Hand-book of Invertebrate Zoology. 



Churchill: Life History of Blue Crab. Bull. U. S. Bur. Fish., vol. 36, 



1919. 



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

 Hay: Life History of the Blue Crab. Rep. U. S. Bur. Fish., 1912. 



PAGURUS (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 

 disturbed? Compare their actions with those in shells. 



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 



x In a fresh specimen the ganglia can be more easily studied after 

 treating them with strong alcohol or Schaudinn's fluid for a moment. 



