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 4 1’étude du Developpement et de la Maturation 
des ceufs chez Hydatina Senta. La Cellule, XIV. 1898. 
Mavpas, M. Sur la multiplication et la fécondation de l’Hydatina senta, 
Ehr. C.R. Ac. Sc. Paris,,CXI. 1890. 
‘Sur la fécondation de l’Hydatina senta, Ehr. C. R. Ac. Sc. Paris, 
CXI. 1890. 
Sur le déterminisme de la sexualité chez )’Hydatina senta. C. R. Ac. 
Sc. Paris, CXTII. 1891. 
Nusspaum, M. Zur Differenzirung des Geschlechts im Thierreich. 
Arch, f. mikr. Anat. XVIII. 1880. 
Prate, L. Zur Kenntniss der Rotatorien. Zool. Anz. VII. 
pe zur Naturgeschichte der Rotatorien. Jena. Z. naturw. XIX. 
1885. 
