OBSERVATIONS ON HYDRA G09 



The maceration method has been largely used by Hadzi (4) 

 in his work on the nervous system of Hydra. I cannot, 

 however, confirm all his findings. 



The nervous cells may be roughly divided into two types, (1) 

 the ganglion cells and (2) cells which are more or less inter- 

 mediate in form between the ganglion cell and the epithelial cell. 



The former are of various shapes according to the number 

 of processes they possess (Text-fig. 4, a, c, d, e). The nucleus 

 stains much less deeply with methylene blue than that of the 

 ordinary interstitial cell, as does also the nucleolus. There 

 may be two of the latter. The cell-body usually consists of 

 a thin layer of protoplasm surrounding the nucleus, but it is 

 frequently prolonged at either end into a short thick process 

 before giving off the long nerve-threads. These latter are 

 long thin processes, often branching. Where they branch 

 there is usually a slight swelling, and these swellings are seen 

 along the course of unbranched processes as well (Text-fig. 4, 

 a and d). The processes of one cell can often be seen to unite 

 with those of another, so that the cell-body appears to lie in 

 a network of interlacing threads. Many of the processes 

 apparently end freely, sometimes in a small knob, while others 

 are attached to the muscle-fibres of myoepithelial cells from 

 which they cannot be detached by tapping on the cover-glass 

 or by irrigation under it. The ganglion cells of the body are 

 usually simpler and less branched than those of the head 

 or foot. 



The second type of nervous cell is long and narrow in shape, 

 with the nucleus about the middle of the cell-body, and has 

 a nervous process only at one end (Text-fig. 4, h and/). This 

 may branch and sometimes it comes into connexion with 

 another nervQus cell. The other end is flattened (Text-fig. 4, h) 

 or knob-like. These cells correspond to Hadzi's ' sensory 

 cells ' or ' sensory nerve-cells ', but I have, as a rule, not been 

 able to find a short projecting hair on the flattened end. 

 In one case a knob-shaped end bore two fine hairs each ending 

 in a little swelling, and in several other cases there were one 

 or two short hairs (Text-fig. 4, /). On examining the surface 



NO. 268 S S 



