1892.] Heredity and the Germ-Cells. 653 
each is greatly reduced. 3. That there is no line between 
male and female, the conjugating cells are simply in a similar 
physiological condition wherein’ a mingling of hereditary 
characteristics affords a new lease of life. As Maupas says: 
“ Les différences appelées sexuelles portent sur des faits et 
des phénomènes purement accessoires de la fécondation. La 
fécondation consiste uniquement dans la réunion et la copula- 
tion de deux noyaux semblables et équivalents, mais provenus 
de deux cellules distinctes.” 
In this conclusion as to the secondary and superficial, rather 
than fundamental, difference between the two sexes, Maupas 
simply confirms the views of Strasburger, the botanist, Hen- 
sen, R. and O. Hertwig, Weismann, and others, namely, that 
sex has evolved from the necessity of cell conjugation; that 
even in the higher forms the cells borne by the two sexes are 
absolutely neutral so far as sex is concerned, the wide differ- 
ence of form of the germ-cells is a result of physiological 
division of labor—the mass and yolk of the ovum having 
been differentiated to support the early stages of development, 
while the spermatozoon has dispensed with all these accessor- 
ies and acquired an active vibratile form for its function of 
reaching and penetrating the ovum. The evidence of the 
Infusoria is paralleled among some of the plants, in which 
conjugation between entirely similar cells is observed 
The causes finally determining sex may come surprisingly 
late in development, and according to the investigations of 
Diising and the experiments of Yung’ and of Giron are directly 
related to nutrition. High feeding favors an increase of the 
percentage of females, while, conversely, low feeding increases 
the males. In Yung’s experiments with tadpoles the follow- 
ing results were obtained : 
Females. Males. 
Normal DELOODLARE, aeaa neer irera 57 43 
High nutrition 92 8 
5See Geddes and Thomson: The Evolution ha Sex, 1891, also, Diising: Die 
Regulierung des Geschlechtsverhaltnisses bei d. Vermehrung der Menschen, Tiere 
und Pflanzen, Jen. Zeit. f. Natur., Bd. 17, 1884. : 
