560 LORANDE LOSS WOODRUFF 



excretion products of two less closely related species were favor- 

 able to growth. 



More recently, Warren/^ working with Daphnia magna, noted 

 that, by continued breeding in small aquaria in which the water 

 remained unchanged, the rate of reproduction and the number 

 of young in a brood was markedly decreased, and also that the 

 length of the spine of the carapace was considerably shortened. 

 This result he attributed to the excretion products of the daph- 

 nids and, since ostracods and copepods flourished when the daph- 

 nids were waning, he concluded that the products of metabolism 

 of Daphnia are specifically injurious to Daphnia, 



Little work has been done to determine the effects of limited 

 volumes of culture medium on the reproduction of Infusoria. 

 Balbiani^^ in 1860 briefly reported a single experiment on Para- 

 maeciam from the results of which he concluded that the organ- 

 ism must be in not less than two or three cubic centimeters of 

 infusion for the greatest reproductivity to be realized. Kula- 

 gin,^^ studying the generations of certain infusoria with reference 

 to 'senile degeneration,' suggested that this was due largely to 

 the fact that when the organisms have lived for a number of gen- 

 erations in the same water, they have contaminated the water 

 by the excretion of substances analogous to toxins, and these 

 gradually accumulate until the nuclei are affected. 



The chief products of the destructive metabolism of the infu- 

 sorian are in all probability water, urea, carbon dioxide and 

 various salts, and these are eliminated chiefly by means of the 

 contractile vacuole. A considerable amount of experimental evi- 

 dence as well as analogy with higher forms points to the conclu- 

 sion that CO2 is voided in appreciable quantities by the contrac- 

 tile vacuoles of the Infusoria. For example, Jennings^'' deter- 

 mined that an acid is present in the vicinit}^ of active paramaecia 

 which is not sufficiently strong to attack CaCOs, but which will 



1* Warren, Quart. Journ. Mic. Sci., vol. 43, p. 212, 1900. 



1^ Balbiani, Comptes Rendus de FAcademie des Sci., Paris, T. 50, pp. 1191- 

 1195, 1860. 



18 Kulagin, Le Physiologiste russe, T. 1, pp. 269-279, 1899. 

 1' Jennings, Journ. Physiol., vol. 21, pp. 258-321, 1897. 



