306 GERM-CELL CYCLE IN ANIMALS 
definite position on the spindle at this time, but, as 
indicated in Fig. 82, the distribution of the maternal 
and paternal chromosomes to the daughter cells is 
entirely a matter of chance. If the homologous 
maternal and paternal chromosomes really are dis- 
tributed by chance to the eggs and spermatozoa 
following synapsis, then the number of combinations 
possible are as follows (Sutton, 1903) : 
Somatic Series | Repucep SERIES Coe AN Homainacens 1s. 
2 1 Q 4 
4 g 4 16 
8 4 16 256 
16 8 256 65536 
24 12 4096 16777216 
36 18 262144 68719476736 
The only direct evidence that such distribution 
of chromosomes takes place is that furnished re- 
cently by Carothers (1913) from a study of the 
spermatogenesis of three Orthopterous insects, 
Brachystola magna, Arphia simplex, and Dissosteira 
carolina. Miss Carothers, while working in Pro- 
fessor McClung’s laboratory, discovered a tetrad in 
the first spermatocytes of these insects which consists 
of two unequal dyads (Fig. 83). During the two mat- 
uration divisions the four parts of this tetrad pass 
to the four spermatozoa, and consequently two sorts 
of spermatozoa are produced so far as this chromo- 
some is concerned, one-half with one of the larger 
elements of the tetrad and one-half with one of the 
