138 ARTHROPODA. 



(d) Cut out 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 \Yhich 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. xA.long 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. 



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 



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

 treating them \vith strong alcohol for a moment. 



