THE SPERMATOGENESIS OF DOMESTIC MAMMALS. 371 
the lower forms; there exists a dimorphism in number of chromosomes in the 
somatic as well as the germinal cells of the two sexes. It is highly probable 
that a condition similar to those found in the pig, as regards sex-determina- 
tion, exists in man and in the other vertebrates which possess the accessory 
or x-chromosome.” 
During the resting stage of the spermatogonia usually one, sometimes two 
large nucleoli are invariably present. According to GUyER (710) the chromatin 
nucleolus of the spermatogonia and the accessory chromosome are one and the 
same. WODSEDALEK is of the same opinion as regards the pig (’13) and the 
horse (14). BAcHHUBER (16) also found two or move lige, spherical Karyo- 
somes in the rabbit and believes that these may be two accessory elements which 
can be traced very accurately after the formation of the primary spermatocytes. 
From all appearances of the spermatogonia in the horse one is led to 
believe that the chromatin nucleolus in the spermatogonium is not the future 
accessory chromosome. 
B. SYNAPSIS AND THE REDUCTION DIVISION. 
As already described, in post-synapsis the chromatin spiremes appear in 
about half the original number. From this fact it is conceivable that the 
conjugation of the chromosomes probably occurs during the synaptic stage. 
But it is difficult to determine definitely whether the conjugation of the chromo- 
somes takes place by parasynapsis (side by side conjugation) or telosynapsis 
(end to end conjugation). In vertebrates most of the investigators have 
reached the conclusion that the conjugation of the chromosomes occurs by 
parasynapsis [WINIWARTER (02), SCHREINER (06) and Wrtson (’12)], while 
JORDAN (711) believes that in opossum the first numerical reduction of the 
diploid group of chromosomes occurs by telosynapsis (metasyndesis). 
In the horse there is no evidence of the occurrence of telosynapsis. 
During the synaptic stage the longitudinal duality of the chromatin spiremes 
can clearly be seen and this duality is not the longitudinal split of the 
chromosome as seen in the chromosomes of the somatic cells in other animals. 
From accurate observations, however, it is evident that the longitudinal duality 
is simply due to the parallel arrangement of two univalent spiremes. Nearly 
at the end of the synaptic stage the parallel arrangement of chromatin 
