Internal Factors of Sex Determination 401 
the evidence to see whether, in these cases, sex is determined by 
the kind of division that takes place in the sperm. 
The Formation of Male and Female Producing Spermatozoa 
It has been known since 1836 that two kinds of spermatozoa* 
are present in the snail Paludina, and both kinds have been found 
in the upper part of the oviduct where the egg is fertilized, but 
whether both kinds are functional is not known. Meves has 
studied recently the method of formation of these two kinds of 
spermatozoa. The hair-like spermatozoa resemble the ordinary 
forms of spermatozoa, the worm-like spermatozoa have a long, 
rounded, worm-like shape, as the name implies. In the forma- 
tion of the worm-like form, a peculiar and perhaps a degener- 
ate process occurs. Instead of containing the reduced number 
(seven) of chromosomes, it gets only a single chromosome. 
Two kinds of spermatozoa are also described by Meves in the 
butterfly Pygera. One of the two kinds contains no chromatin 
material whatever. It is headless and perhaps functionless also. 
In addition to these cases giant spermatozoa, double the size 
of the normal ones, have been described in several groups, espe- 
cially in amphibians and birds. They are due to the incom- 
pleteness of one or of both of the spermatocyte divisions, and 
may be only abnormal forms incapable of fertilizing the egg. 
The most remarkable spermatozoa, however, are those in 
which half of the spermatozoa contain one more chromosome 
than the other half. 
Henking discovered in 1890 the presence of a peculiar chro- 
matin-like body in the spermatogenesis of the bug Pyrrhocoris. 
It has since been shown that this body is a true chromosome, 
although it behaves differently from the other chromosomes in 
certain respects. The more recent work of McClung, Mont- 
gomery, Paulmeier, Sutton, Stevens, and especially of Wilson, 
has cleared up some of the most important questions connected 
with the behavior of the accessory chromosome. 
' Discovered by von Siebold. 
2D 
