162: . The American Naturalist. [February, 
spermatocytes have also this same half-number after their first and 
second divisions; with some interesting exceptions the sperm and the 
polar body and the female pronucleus have the same number, in any 
species, and this is half the number of other cells of that species. 
With the aid of a diagram the author emphasizes the close parallel 
between the formation of sperms and polar bodies. Starting from a 
mother cell with, say 24 chromosomes, a reducing division forms two 
sperm mother cells, or in the female an egg and a polar body, in each 
of which are only 12 chromosomes, and these are half of the original 
24, unchanged or undivided individually. A second division of each 
cell results in the formation of four sperm mother cells or in the 
female of three polar bodies, and the remaining egg, in each of which 
are 12 chromosomes. These, however, are formed by an equal divis- . 
ion, that is, from the previous 12, 24 arise by a division of each—not 
by the separation of the whole set into two sets as in division with 
reduction. Later the 12 chromosomes of a sperm may be added to the 
12 of the egg nucleus to make the normal 24 of the cleavage nucleus, 
whence, by equal division, all subsequent cells have 24 also. Likewise, 
in the insects, one polar body may unite its 12 with the 12 of another 
polar body. 
Utilizing the recent researches of Guignard, the author draws & 
most interesting comparison between the processes taking place in 
insects andin plants. Without the aid of diagrams this can scarcely 
be rendered intelligible ; the most novel part, however, is an attempt 
to explain the polar bodies of animal eggs as, in a sense, “ larval 
organs,” somewhat comparable to rudimentary structures within the 
embryo sac of a flowering plant. 
The fact that in insects the polar bodies may remain within the egg 
and that they, or their descendants, may unite with one another, seems 
to form a parallel to what takes place in the flowering plant. As 1$ 
well-known, the embryo-sac cell forms two sets of each 4 nuclei within 
its substance, 4 lower antipodal cells and 4 upper cells, of which one 
is the ovum. 
The formation of these is directly comparable to the formation of 
polar bodies in the animal—supposing a second series of divisions to 
supervene and convert the 4, ovum and three polar bodies, into eight. 
In the embryo-sac a remarkable fusion takes place between one of the 
antipodal nuclei and the sister cell of the ovum; this union forms the 
endosperm. Compared with the insect, this union is like the fusion of 
polar bodies, only in a later generation. In the insect nothing appa 
See this Journal, May, 1892. 
