The Prophase in the Ovigenesis and the Spennatogenesis of Planaria etc. 441 
I have not been able to obtain material showing tlie oocytes in 
a stage later tban sbown in Fig. 16, and therefore am not able to 
give figures of the heterotype gemini, but doubtless tliey do not differ 
from tliose of the male cells, which will now be described. 
PART II: — Spermatogenesis. 
Receutly the spermatogenesis of PL gonocephcda bas been worked 
out by Schleif (’07) as far as the earliest stage in the formation of 
the spermatid. 
In vievv of the fact that bis Interpretation of the spermatogenesis 
is the same as for the ovigenesis, it will not be necessary to refer 
to his results witli reference to the formation of the gemini &c., as 
the criticisms advanced above apply witli equal force liere. But 
he has overlooked a very important stage, the resting stage of the 
2nd. meiotic division, which will be described in its place. I have 
also been able to work out the later changes in the spermatid, leading 
up to the formation of the free Spermatozoon, which he does not 
describe at all. 
The earlier stages Figs. 23 — 27 of the Ist. meiotic division of the 
spermatogenesis differ but little from tliose described in the ovigenesis. 
The resting stage (Fig. 23), shows a nucleus in which there are 
numerous chromatin granules connected together by a tliin linin network. 
There is also a nucleolus. Contrary to the experience of Schleif 
with PI. gonocephcda, in PL lactea the achromatic linin network and 
the nuclear membrane are clearly visible. The formier is hardly stained 
in haematoxylin preparations, which perhaps accounts for Schleif’s 
inability to recognise it, as he used only haematoxylin with Bordeaux 
red and Pierocarmine as counter stains. But the nuclear membrane 
is always clearly visible even with haematoxylin, and how he failed 
to see it is unajccountable. 
The nucleolus very soon disappears, for there is no sign of it in 
the leptotene nuclei (Figs. 25 and 26). The cytoplasm of the sperma- 
tocytes, is very different from that of the oocytes. At no time do 
we see in it that coarse fibrillär structure which is so characteristic 
of the latter, and up to the telophase of the Ist. meiotic division only 
one chromatin body (cb Fig. 32) is to be seen in it. 
The earliest stages (Figs. 24—28) of the spireme are precisely 
the same as in the ovigenesis. The synapsis (Figs. 29 — 31) however 
is not so marked as in the latter, that is, the spireme Segments seem 
