Smallwood and Rogers, Molluscan Nerve Cells. 71 



nutiitive conditions under which the animal is placed. The 

 changes in appearance, however, of the nerve cells are so slow 

 that it has been necessary for us to extend our observations over 

 a period of two years in order to satisfy ourselves of their correct- 

 ness. Specimens have been taken from their natural habitat at 

 various times of the year, have been kept in the laboratory under 

 fairly constant conditions, have been fed or starved as we wished, 

 and have finally been killed and their nerve ganglia examined. 



In the summer and autumn specimens, these golden brown 

 bodies are rounded granules of somewhat irregular shape, and 

 varying in diameter from i to 5 //. In specimens kept in the warm 

 laboratory for a considerable time (up to three months) without 

 feeding a distinct change is noticed in the appearance of the cells. 

 The pigment bodies become distinctly smaller, in some cases 

 becoming so small as not to be easily distinguished from each other 

 even with the tV inch oil immersion lens. Under these conditions 

 it is of course impossible to measure them. No bodies as large 

 as 5 ^ were found at all and only an occasional one so large as 2 [x. 

 The substance is in the process of being broken down. It becomes 

 very finely divided and seems to become actually less in amount in 

 the cells. These changes take place so slowly that it is a difficult 

 matter to follow them and only by a long series of observations can 

 one be at all sure of any change in the condition of the pigmented 

 matter. 



In specimens taken early in the spring, which have passed the 

 winter in hibernation, the bodies are not as a rule numerous, though 

 some still remain in the cells. Judging from the appearance of 

 the nerve cells of animals which had been kept in the warm labor- 

 atory during most of the winter and those which were taken early 

 in the spring, it would seem that the processes of metabolism had 

 been much greater in the specimens kept in the warm room and 

 that the total amount of matter stored up was in both cases some- 

 what in excess of the amount which would ordinarily be needed 

 for the use of the cells. 



Fatigue. — On account of the fact that this snail, like many 

 others, withdraws into its shell when disturbed, it was found impos- 

 sible to subject it to the same conditions for producing fatigue as 

 in the case of Limax. It was possible to remove the ganglia, to 

 place them upon a slide between electrodes and to stimulate the 

 nerve cells directly by means of induction currents. As a result 



