OBSERVATIONS ON HYDRA 611 



of a deeply stained Hydra with an oil-immersion lens, 

 I have not been able to find any number of projecting hairs 

 (apart from the cnidocils) such as one would expect if sensory 

 cells bearing hairs played a large part in the stimulation of the 

 Hydra. 



I have also tried Hadzi's vital methylene blue method (4) 

 but without success. Hadzi states that his method gives good 

 results only with H. viridis and in sunshine. In my 

 specimens the nematocysts took up the stain strongly and the 

 ectoderm faintly, but there was never any differential staining 

 of the nervous elements. 



It is considerably more difficult to recognize nervous cells 

 in section, since the processes are cut short. Hadzi figures, 

 and describes as nervous, cells which stain more deeply than 

 the other interstitial cells and lie basi-epithelially, sending 

 processes to the surface and in other directions. I have seen 

 such appearances in section, but find it impossible to say 

 whether these apparent threads are not merely strands of 

 protoplasm belonging to the myoepithelial cells, or cut edges 

 of cells. I have not found the sensory apparatus which he 

 describes at the surface. 



The nerve-cells probably originate from interstitial cells. 

 Some of the latter may often be found connected to one 

 another by short strands, and interstitial cells with short 

 or long processes are not uncommon especially in the tissues 

 of newly hatched Hydras. These differ little from the nervous 

 cells except in their nuclei and in the larger amount of cell 

 protoplasm which they possess. 



The effect of various nerve poisons was tried. 



Chloroform. — A weak solution of chloroform in water 

 (which ana,esthetized a Daphnia completely in a few 

 minutes) caused a curious rhythmic contraction. The animal 

 contracted down into a tight spiral quickly, and then slowly 

 straightened out again. This was repeated at intervals which 

 gradually increased from about two minutes up to fifteen or 

 twenty minutes. Eventually it became motionless and insensi- 

 tive to contact. This occurs in two hours or longer, after which 



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