EXPLANATION OF PLATES 



All the figures have been drawn with the Abbe camera lucida, carried either on the 

 microscope, or on the Giltsch-Zeiss support. The drawings have been reproduced by photo- 

 graphy, in order to secure the maximum of accuracy in outline. 



In comparing these drawings with those of Grassi, Hertwig, etc., it must be remembered 

 that in many cases they had the advantage of working on living material. 



There are no figures corresponding to the numbers 24 — 29. 



g. = ganglion. p.c. = pulp-cavity. 



