350 Experimental Zoology 



female summer eggs. Early fecundation and scarcity of food 

 during the time of development of the ovary lead to winter eggs, 

 from which only females emerge. 



Lauterborn has found in another species of rotifer, As- 

 planchna, that the same individual may contain a winter egg 

 and male embryos. This is strong evidence in favor of the view 

 that the male eggs and the winter eggs are the same, as Maupas 

 inferred for Hydatina. The result recalls the somewhat similar 

 observations of Issakowitsch on daphnia, where, however, the 

 winter egg and the males appear consecutively. Lauterborn, 

 following Weismann's idea for the daphnias, thinks that in roti- 

 fers, other than Hydatina, external conditions do not determine 

 the sequence of parthenogenetic and sexual generations. Each 

 species has a more or less definite number of generations in the 

 parthenogenetic part of its cycle, but he brings forward no 

 experimental evidence in support of his conclusion. 



LITERATURE, CHAPTER XXII 



LAUTERBORN. Ueber die zyklische Fortpflanzung limnetischer Rotatorien. 



Biol. Centrbl. XVIII. 1898. 

 LENSSEN. Contribution a 1' etude du Developpement et de la Maturation 



des ceufs chez Hydatina Senta. La Cellule, XIV. 1898. 

 MAUPAS, M. Sur la multiplication et la fecondation de 1'Hydatina senta, 



Ehr. C. R. Ac. Sc. Paris, CXI. 1890. 

 Sur la fecondation de 1'Hydatina senta, Ehr. C. R. Ac. Sc. Paris, 



CXI. 1890. 

 Sur le determinisme de la sexualite" chez 1'Hydatina senta. C. R. Ac. 



Sc. Paris, CXIII. 1891. 

 NUSSBAUM, M. Zur Differenzirung des Geschlechts im Thierreich. 



Arch. f. mikr. Anat. XVIII. 1880. 

 PLATE, L. Zur Kenntniss der Rotatorien. Zool. Anz. VII. 



Beitrag zur Naturgeschichte der Rotatorien. Jena. Z. naturw. XIX. 



