106 MOLLUSCA. 



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. 



AMPHINEURA. 



CHAETOPLEURA. 



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 

 finger in its back and prevent it from curling for a minute. It 

 will then generally remain attached to the slide and may be 

 studied from both sides. 



3. How many plates are there? What is the shape of each? 

 Do they apparently join edge to edge or do they overlap? Do 

 the plates extend clear to the margin of the animal? What 

 reason is there for having plates instead of a solid dorsal shell ? 



4. Notice the thickened margin of the animal, and see that 

 dorsal ly it bears spicules, while ventrally it is smooth and is 

 applied closely to the slide. 



