470 
J. BRONTfc G-ATENBY. 
A very important point to notice is that degeneration of the 
nucleus may occur at any stage, but in some species it tends 
to .take place at certain special stages. It should be men- 
tioned that in different bundles the individual spermatids all 
tend to reach the same stage of development, degeneration 
appearing at one and the same time throughout. Some 
spermatozoa get further than others in development, and 
apparent arrival at the last step of sperm-formation does not 
necessarily mean that the canker of degeneration may not 
appear later when the sperm has entered the egg. Thus 
development might be initiated by such spermatozoa without 
the male nucleus being able to fuse. But I do not believe 
that the so-called “apyrene” sperm could enter the egg, 
though the suggested effect of an a apyrene ” sperm might 
be got by degeneration overtaking a normally constituted 
spermatozoon at some stage in fertilisation. If a spermato- 
zoon entered an egg, if its nucleus began to lag, as it often 
does in spermiogenesis, and if the centrosome acted normally, 
one might possibly get development initiated, and there is no 
doubt that every sperm from the same bundle would act 
likewise. There is nothing illogical in the thought that if 
degeneration can overtake the sperm at any stage of sper- 
matogenesis, it could also overtake it at any stage in fer- 
tilisation. 
In PL 26, fig. 14, I have drawn a degeneration stage in 
PygBBra bucephala. The nuclei have shrunken into 
darkly staining lumps, as is usually the case when any 
nucleus degenerates completely. Even after this stage a 
partial elongation of the cell may take place. 
The Mitochondria. 
In my previous paper I stated that it was impossible to 
make out the relationship of the macromitosomal spireme 
(nebenkern) and the centrosome. By means of degenerate 
stages such as those drawn in PI. 26, figs. 3 and 11, it is clear 
that the macromitosome consists of a spireme, the front free 
end of which is attached to the centrosome. The abnormal 
