RETARDING INFLUENCE OF CROWDING 123 



mals, which must have brought them into violent contact with the 

 walls of the capillary tubes. 



Crampton's work was in many ways an extension of Conklin's 

 earher observations concerning the size attained by the gasteropod 

 Crepidula plana with relation to the amount of available space. The 

 dwarfing of these snails when crowded, Conkhn thought, should be 

 interpreted as due to space inhibition of cell division. 



These facts were reported by Conklin in 1898. Crepidula plana 

 lives within the shells harboring herinit crabs. If the shells are small, 

 the contained Crepidula are few in number and are dwarfed; if 

 large, the Crepidula may be present in numbers and be large. Since 

 there may be but i small individual in the small shells, while there 

 may be 4 "giants" in a large one, Conklin believed that the difference 

 in size is not due to differences in available food; nor is it due to the 

 presence of accumulations of excreta, since both shells are equally 

 open to the surrounding ocean. Neither is the result due to the lack 

 of room to move about in, since both large and small Crepidula are 

 relatively firmly attached to their substratum. Rather, there is a 

 space retardation of cell division, since the cell sizes of the one are no 

 larger than the other. If the small Crepidula are transferred to a 

 larger space, they will increase in size. The stimulus acting to retard 

 cell division in these dwarfed Crepidula is more obscure than in the 

 case of the rapidly darting Paramecium confined in a capillary tube. 



Kalmus (1929) has added two other factors to Crampton's three, 

 in reporting his own studies on the effect of inclosing Paramecium 

 caudatum, Stylonychia, and Spirosiomum in capillary tubes. He finds 

 that the age of the culture and the solubihty of glass in the culture 

 medium have decided effects. 



Capillary tubes made of two kinds of glass were used: "Schot- 

 schem, nr. 20" and the Bohemian glass made by CavaHer. The tubes 

 measured 100-200 /it and the length of the contained column of hquid 

 was from 8-30 )U. Some of the observations are summarized in 

 Table I. These results and others show that the type of glass in 

 which small amounts of culture medium are held may affect the con- 

 dition of the contained animals. 



Kalmus concludes that his observations show that the retardation 



