Chromosomes in the Sexual Cells. 
99 
w ( — egg-nucleus) 
x ( = second polar body). 
That the formation of the tetrads is accomplished in the 
manner above mentioned is clearly shown, chiefly by the 
observations of vom Rath and Riickert. I myself shall 
shortly be able to demonstrate the process by a specially 
typical case, and to show that, even if there exist certain 
variations, the principle of the process remains the same \ 
Thus it is permitted to assume, as a matter of fact, that 
reduction-divisions exist in the generative cells of animals. 
It may be even asserted as highly probable that their occur- 
rence in the formation of the ova and spermatozoa of animals 
is a general phenomenon 2 . Thus it is a fact that at present 
the observations of the botanists and zoologists do not agree 
at all, and therefore cannot form a common basis for theo- 
retical conclusions. 
In making a generalizing theory, however, one is either 
obliged to enforce the observations of the one or the other 
side, or at least to assume incompleteness of observation. 
The zoologist will propose to himself two questions : first, 
if perhaps some of the figures given by botanists resemble 
the processes of reduction observed in animals, so that it may 
be assumed that the botanists have possibly overlooked certain 
stages ; and, secondly, if the kind of direct diminution of the 
chromosomes, as described by the botanists, is also to be 
observed in the generative cells of animals. 
With regard to the first question I venture only to make 
one supposition. The figures which Guignard 3 has given for 
the first division of the pollen-mother-cell (compare Figs. 12, 
1 Compare Die Vorstadien der Eireifung, Arch. f. mikr. An., V. 45, 1895. 
2 There is at the present day only one observation which directly opposes this 
generalization. Compare A. Brauer, Zur Kenntniss der Spermatogenese von 
Ascaris megalocephcila, Arch. f. mikr. Anat., V. 42, 1893. 
3 L. Guignard, Nouvelles etudes sur la fecondation, Ann. d. sc. nat., Bot., 
1891. 
II 2 
