1892.] Heredity and the Germ- Cells. 655 
given off independently of, and prior to, the contact of the 
spermatozoon, and, finding in the leeches that the first polar 
body subdivides to form two bodies, he considered them as 
formed by true cell division, and containing both nucleoplasm 
and chromatin. Giard independently reached a similar opin- 
ion, assigning an atavistic meaning to the polar cells. Whit- 
man, in 1878, advanced the idea that they represented ves- 
tiges of the primitive mode of reproduction by fission, while 
Mark described them as “ abortive ova.” 
At this point speculation subsided until it was revived by 
Weismann’s attempt to connect these bodies with his theory 
of heredity,’ already referred to. The whole history is clearly 
iven in R. Hertwig’s masterly memoir upon Ovo and Sper- 
matogenesis in the Nematodes.” Taking advantage of Boveri’s 
discoveries in staining technique, and stimulated by Weis- 
mann’s prediction that spermatozoa would also be found to 
extrude polar bodies, this author examined all stages in the 
peculiarly favorable germ-cells of the thread-worm of the 
horse (Ascaris megalocephala). 
He made the surprising discovery that ova and spermato- 
zoa are formed in a substantially similar manner by repeated 
divisions, the single difference being that the last products of 
division among the sperm-cells are effective spermatozoa, capa- 
ble of development in fertilization, while the last products of 
division in the ovary are, first, the true ova, and second, the 
abortive ova (polar cells) incapable of development. In both 
ova and spermatozoa the nucleus contains but one-half the 
chromatin which a typical nucleus contains; in the case of 
A. megalocephala each of the germ-cells contains but two chro- 
masomes while the normal body-cells contain four. The man- 
ner in which this maturation of the germ-cells for conjugation 
is brought about is beautifully shown in these diagrams, taken 
from Weismann’s essay, “ Amphimixis.” You observe that 
the number of chromasomes in the primary germ-cells is four 
(figs. 11 and 12, A). Then are formed by subdivision the ovum 
and sperm “ mother-cells,” in which the chromatin substance 
tOn the Number of Polar Bodies and their Significance in Heredity. 1887. 
TEi- und Samenbildung bei Nematoden, Archi. mikr. Anat., Bd. 26, 1890. 
