THE SPERMATOGENESIS OF DOMESTIC MAMMALS. 381 
until the granular appearance is entirely lost, and the cell enters into a 
prophase stage. Longitudinal splittings of the chromosomes thus formed now 
become clearly visible (Fig. 24), and can be seen till the late prophase (Fig. 
25). It is difficult to determine whether the spireme is not continuous, as 
stated above, but it is very probable that it is so, as the end of each chromo- 
some can be easily dis‘inguished throughout the entire stage (Fig. 22—24). 
The spiremes continue to become shorter and thicker, until they assume short 
rod shapes (Fig. 25). Sometimes the nucleoli still remain among the chromo- 
somes in the late prophase. It is, however, difficult to distinguish them in 
the preparations stained with iron-haematoxylin, while they can clearly be 
seen in those stained with ZIMMERMANN’S method. 
In the polar view of the equatorial plate of the metaphase the number 
of chromosomes may be counted as thirty three, most of which are arranged 
‘adially around a central space (Fig. 28). 
As many authors have already pointed out in insects and other animals, 
the chromosomes of the spermatogonia in every stage vary considerably in 
size and form (Figs. 28, 29, 37, 38). In the diploid groups, as shown in 
Figs. 29 and 38, the chromosomes are found to correspond two by two. 
These can clearly be seen in the metaphase plate of such cells as shown in 
Figs. 28, 37. Among the chromosomes of these cells the three largest ones 
can easily be distinguished. From the size and form of these chromosomes, 
it is evident that one of them has no mate, and this odd one is evidently 
an accessory chromosome. Every chromosome now simultaneously divides 
into two portions along the longitudinal split already described in the 
spireme stage, no special chromosome with different behavior being seen 
among them (Figs. 26, 27), although according to WODSEDALEK (14) the 
accessory chromosome in the horse, as a rule, divides a little in advance of 
the ordinary ones. 
At the telophase the chromosomes are not fused, but are so closely appose 
to each other that they can not be clearly distinguished. Later on the nuclear 
wall reappears, and the chromosomes become separated from each other (Fig. 
30), their individuality thus becoming again clearly distinguishable. No | 
chromosome of this stage shows any longitudinal splitting (Fig. 30). 
Spermatogonia in adult animals :—As in the horse, in the testes of adult 
