350                       Experimental Zo'dlogy

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 brjngs 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 oeufs chez Hydatina Senta.    La Cellule, XIV.    1898.
Maupas, M.    Sur la multiplication et la fecondation de I'Hydatina senta,
Ehr.    C. R. Ac. Sc. Paris, CXI.    1890.
Sur la fecondation de I'Hydatina senta, Ehr.    C. R. Ac. Sc. Paris,

CXI.    1890.
Sur le determinisme de la sexualite chez I'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,