130 MOLLUSCA. 



throughout their length. Slowly pry the valves apart, lift up 

 the free end of the foot and pull it posteriorly. 



The cerebral ganglia are plainly visible without further cutting. 

 They lie just posterior to the anterior adductor muscle and in front 

 of the mouth, and are widely separated. They are connected by 

 a narrow commissure, and each gives rise to a cerebro-visceral 

 and a cerebro-pedal connective and to a number of nerves. The 

 nerves that supply the anterior part of the mantle and the ante- 

 rior adductor muscle are especially easily seen. 



5. If the specimen is one that is nearly or quite dead, it is, 

 by cutting, easy to follow the cerebro-pedal connectives to the 

 pedal ganglia, which are not far from the base of the foot and 

 not deeply embedded. 



6. Allow the foot to return to its normal position and cut 

 along the line of union of the inner gills. Without further cut- 

 ting the visceral ganglia may be studied. Their connectives, 

 which may be followed easily as far forward as the palps, and 

 the posterior pallial and the branchial nerves may be seen. 



A drawing of the nervous system should be made. 



Drew: The Habits and Movements of the Razor-shell Clam, Ensis direc- 



tus. Biol. Bui., 12, 1907. 

 : The Physiology of the Nervous System of the Razor-shell Clam, 



Ensis directus. Jour. Exp. Zool., 5, 1908. 



AMPHINEURA. 



CHAETOPLEURA. (Chiton.) 



It will be profitable to study only external features, unless 

 time is to be had for cutting and studying sections, as the species 

 is small and difficult to dissect. Its apparently generalized struc- 

 ture, and its adaptations, make it desirable for students to under- 

 stand from descriptions and figures the main features of its an- 

 atomy. 



1. Examine specimens that are attached to stones and shells 

 and see how nicely they adapt their shapes to the shapes of the 

 objects to which they are attached. How is this possible? 



2. Remove a specimen and quickly transfer it to a clean 

 glass slide, applying its ventral side to the glass. Put your 



