THE SPERMATOGENESIS OF DOMESTIC MAMMALS. 391 
94). The two centrosomes can thus be distinguished as a proximal and a 
distal, the former at the same time comes to be placed close to the nuclear 
wall (Fig. 93). Meanwhile a fine filament is seen to proceed from the distal 
centrosome backward towards the surface of the cell, which later becomes the 
axial filament of the spermatozoon (Figs. 93, 94). This seems to indicate 
that the axial filament is mainly developed from the distal centrosome which 
corresponds to the outer centrosome in the horse. 
The idiozome which has appeared in the resting spermatids, gradually 
diminishes in size, becoming more and more homogeneous (Figs, 86, 88, 89). 
When the nucleus begins to migrate towards one side of the cell, the idiozome 
which remains close to the nuclear wall, moves to a point directly opposite 
to the centrosome in contact with the nuclear wall (Figs. 88, 89). From 
these phenomena it is evident that the archosome is formed from the idiozome 
as indicated by MEVEs. 
Simultaneously with the migration of the idiozome, a slight depression 
can be detected on Ithe anterior part of the nuclear wall (Fig. 92). The 
archosome finally becomes fixed as a small spheric body at this point, just as 
WODSEDALER (713) has shown to be the case in the pig. 
In the daughter cells of the secondary spermatocyte the mitochondria still 
lie scattered in the cell body. Afterwards they commence to gather around 
the centrosome (Fig. 91). In the horse, the main portion of the mitochondria 
in the final development of the spermatozoa fuse and form a mass which 
is similar to a “Nebenkern ” in insects. During the final transformation 
of the spermatid a portion of the mitochondria is located at the posterior 
part of the cell where it encloses the axial filament and the centrosome (Figs. 
91, 93, 95), the rest of them are probably cast off, out of the body of the 
spermatozoa (Fig. 95). In the mature spermatozoa the mitochondria come to 
occupy the middle part of the spermatozoon (Fig. 98). 
Most of the chromatic material now collects increasingly at the peripheral 
part of the nucleus (Figs. 88—92). In the development of the spermatozoa 
neither the chromatin nucleolus nor the true nucleolus (plasmosome) can be 
seen (Figs. 85—94). According to JorRDAN (711), in opossum a conspicuous 
central plasmosome appears during the trausformation of the spermatid. 
With the changes of the nucleus, the tail becomes more and more 
