THE SPERMATOGENESIS OF DOMESTIC MAMMALS. 385 
constriction can, however, be traced during the whole diplotene stage (Figs. 
54—57). 
Later on the spiremes shorten and become condensed, assuming straight 
or bent rods; the surface of each chromosome remains, however, rough and 
somewhat filamentous, until they arrange themselves in the metaphase plate 
(Figs. 57, 63). As in the case of the horse, the rings or loops of the 
chromosomes do not appear in the late prophase, but in strongly decolourized 
preparations the longitudinal split of the chromosomes appears very distinctly 
(Figs. 56, 57). During the prophase, it is impossible to count the number of 
chromosomes accurately, since they never lie in a plane but overlie one another 
(Figs. 55—57). 
The chromosome nucleolus :—In the beginning of the leptotene stage one 
of the chromosomes does not grow to a fine chromatin filament but remains 
in its original form, while the others develop to the leptotene threads. 
During the synapsis it can not be recognized, which is to be accounted for 
by the fact that it usually takes its position within the entangled mass of the 
chromatin spiremes. ; 
While the ordinary chromosomes now become less compact and stain 
. more faintly, this chromosome ‘retains its staining capacity and its sharp 
contour (Figs. 43, 53). From this stage (pachytene stage) until the Inte 
prophase it usually remains in contact with the nuclear wall and generally 
appears oval, varies in size and form, sometimes heart shaped, occasionally 
bepartited (Figs. 53—55). During the prophase it stains like the chromatin 
spiremes with ZIMMERMANN’S method. Its behavior and its form correspond 
almost exactly with the accessory chromosome or the chromosome nucleolus 
of the horse. | 
In the late prophase, when the ordinary chromosomes have assumed rod 
shape, the chromosome nucleolus is situated within the ordinary chromosomes, 
but it can be identified by its shape and behavior. 
The cytoplasmic structure :—The cytoplasmic structure, with the exception 
of the idivzome and the mitochondria, can not be identified, but in the horse 
one or two small chromatoid corpuscles make their appearance during the 
growth period. 
In the early diplotene stage when the spiremes are spread throughout the 
