PAGURUS. 167 



4. Cut oiit the alimentary tract, open the stomach, and 

 examine the grinding and straining apparatus. 



Make a drawing of the alimentary canal. 



Excretory Organs. — Examine the antennary gland (green 

 gland) on the inside of the carapace opposite the base of the 

 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 



antenna. 



Nervous System.— Find the ring of ganglia around the 

 ventral end of the sternal artery.* Trace the nerves from this 

 to the appendages and to the small abdomen. Trace the circum- 

 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. 



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



1919. 

 Gurney: Metamorphosis of Corystes. Quart. Jour. Micro. 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 lost4ts symmetry in appendages as well as in 

 shape? 



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

 is the function of these appendages? 



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

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



