244 ^- D- WHITNEY. 



of the hydras that were sectioned and studied. They always 

 seem to be free in the enteric cavity but sometimes they are 

 mixed with a substance which resembles the granular contents 

 of the endoderm cells. No free endoderm cells were ever seen 

 in the enteric cavity. 



Professor W. J. Gies was kind enough to perform some experi- 

 ments for me in which blood corpuscles were put into a 0.5 per 

 cent, solution of glycerine made with physiological salt solution. 

 Upon measuring the diameters of the corpuscles both before and 

 after putting them into the glycerine solution it was determined 

 that if there was any change it was a slight shrinkage but never 

 any enlargement of the corpuscles. 



When these results of the effect of glycerine on blood corpus- 

 cles are compared with those obtained on the endoderm cells of 

 hydras which were also kept in the same percentage of glycerine 

 solution it is seen that the results are opposite — the corpuscles 

 shrink and the endoderm cells become larger. 



The shrinking of the corpuscles is probably due to an increase 

 of the osmotic pressure of the solution caused by the addition of 

 the glycerine and is purely a physical change. 



The enlargement of the endoderm cells of hydras might be 

 explained as due to the glycerine acting as a stimulus to the cell 

 and causing certain vital processes in it to become active which 

 result in a large and rapid absorption of water by each cell. The 

 cells react to this stimulus as long as the animals are kept in the 

 glycerine solution. Thus this change could be called a physio- 

 logical one brought about by the stimulation of living processes 

 in the cells. 



Some cells were seen which had little protuberances or out- 

 pocketings on their inner free ends which looked as though they 

 might be weak places in the cell wall that were forced out by 

 the increasing pressure from within. Doubtless the ruptures 

 occur at these places. 



As it is a well-known fact that hydras have extraordinary 

 powers of regeneration in the closing of wounds, as when their 

 bodies are cut into two or more parts, and also in the replacing 

 of lost parts, the assumption that the ruptured places in the endo- 

 derm cells close and grow together quickly is not, I think, an 

 mprobable assumption. 



