ON SPERMATOGENESIS IN THE RAT. 
347 
being surrounded by a small amount of protoplasmic material. 
The dark granules are not derived from the destruction of 
nuclei, but make their appearance in the protoplasm of the 
developing spermatozoa at a certain stage of their develop- 
ment, and are cast off, together with a small amount of unaltered 
protoplasm, when the development is nearly completed. They 
appear to consist of a mixture of albuminous and fatty 
material, since in osmic acid preparations their place is taken 
by a cluster of minute black granules (fig. 15). 
A very different appearance is presented by sections prepared 
by the chloride of gold method (figs. 12, 13, 14). A stage of 
development corresponding to fig. 1 is represented by fig. 12 ; 
in this preparation the nuclei are entirely unstained, and 
resemble clear vacuoles, but the protoplasmic structures and 
cell-outlines are rendered very conspicuous. The large growing 
cells of the second layer are seen to contain large granules — 
the “accessory corpuscles” of Henson — which are darkly 
stained by the reagent (fig. 12, b"), and in the small cells of 
the outer layer similar but smaller bodies are seen. The 
young spermatozoa which form the third layer, also each 
contain an accessory corpuscle, which at this stage is embedded 
in the protoplasm at the inner part of the cell (fig. 12, c). 
The fully formed spermatozoa (fig. 12, d) show an obvious 
division into three parts, head, body or middle piece, and tail. 
The tail is entirely unstained, but the middle piece contains a 
spiral filament which is darkly stained, and consequently very 
conspicuous. It winds in a close spiral round a slightly tinted 
core, which is continuous with the tail of the spermatozoon. 
noticed ; they are produced, not by the destruction of nuclei, but from the 
protoplasm of the developing spermatozoa, from which they separate off at a 
late stage of their development. They are of great interest, since they 
appear to represent the polar globules of the ovum, and their separation 
possibly means the separation of the female element from the 
spermatozoa. They are, I believe, constant in mammalia ; although owing 
to the shortness of the middle piece of the spermatozoon in most animals 
e.g. the dog, rabbit, man, their separation cannot be made out with such 
distinctness as in the case of the rat. 
