96 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Auditory Cells. — (figs. 98-1 11.) In a previous paper 

 (Eisen i>9) the auditory cells have already been described 

 in detail. After these investigations were completed, how- 

 ever, a few very young specimens of Pontoscolex from 

 Tahiti were received through the courtesy of Mr. Alexander 

 Craw. As the worms were alive when brought to me, 

 opportunity was afforded for careful fixing, and the study 

 of these specimens has enabled me to settle some points 

 which were left in doubt in the former paper. Especial 

 reference is made to the very minute structures found in 

 every auditory cell, which the author described as nerve- 

 endings or nerve-plates. This decision does not now appear 

 to be correct, however. The new methods of fixing have 

 made it possible to more clearly demonstrate their minute 

 structure. 



In a former paper on the blood of Batrachoseps (Eisen 

 21) the name archosome was suggested for the structure 

 composed of centrosome and spheres, and in the following 

 descriptions this term will be used to designate the struct- 

 ures which were at first supposed to be nerve-plates. They 

 are not situated on or at the surface of the cell, but in its 

 interior, about half way between the nucleus and the cell- 

 wall. The archosomes are of varying size: some are very 

 small (possibly due to a state of shrinkage) and show no 

 interior structure ; others are comparatively large and are 

 distinctly differentiated. The largest archosomes appear 

 as a flat disc, as large or larger than the nucleus of the 

 cell. Between these two extremes there is a series of inter- 

 mediate sizes and forms. But, small or large, the archo- 

 somes always appear to be surrounded by a defining mem- 

 brane which is very sharply defined in the largest of them. 

 The archosomes, even in the small cells, are frequently 

 unequal both in size and form (figs. 100, loi) ; more rarely 

 they are of the same size (figs. 99, 109, 102, 106). 



In each archosome there are nearly always two defin- 

 able zones, one interior to the other. The outer of these 

 zones, which is much the larger, I identify as the archo- 

 plasm or centrosphere (Eisen 20). In this sphere there 



