The spermatogenesis of Hydra. 409 
The variations in size of the various cells taken at the equa- 
torial plate stage and including only those spherial or nearly so is 
as follows: 
Spermatogonia 10.2 u to 9 wu in diameter 
Spermatocytes 1st order Kae, ON 
s onde, SS) ey ton DIRE, 7" 
Spermatids EIS et LUDO 
As before mentioned, by considering extreme sizes we might 
introduce another generation of spermatogonia which would allow 
of a growth period in the transition from spermatogonia to sper- 
matocytes of the first order, thus: 
Diameter Relative volume 
Interstitial cells 13770 2197 
Spermatogonia 1st generation NOR 1061 
i 2nd N Large 457 
2 drd x D'OR 206 
which would grow to 
Spermatocytes of 1st order Are 405 
The other generations would remain as before. But the com- 
plete absence of transition sizes from 5.9u to 7u except a few 
exceptional cases between 6.7 and 7u seems to nuilify this hypo- 
thesis. The entire process of spermatogenesis is so hasty in Hydra 
that it seems impossible moreover that there should be a prolonged 
pause and grown at any stage. The series of measurements for 
the cell generations as given seems to be marked by a regularity 
that commends its probability. 
Nutrition of the spermary. 
We should naturally connect these changes in size with meta- 
bolic changes. That such are going on cannot be doubted. During 
the formation of the spermary there is a great increase of the volume 
of tissue. Cells are dividing and the daughter cells growing at a 
rapid rate. Especially is nucleinic material used during the process, 
for the nuclei of the interstitial cells are relatively very large, and 
it will be remembered, during the prophase they are rapidly growing, 
while the cell body diminishes in size. As already noted a marked 
character of the cells of Hydra during spermatogenesis is the vacu- 
olate condition. Fig. 14 and 15 have already been contrasted, — 
