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ON FECUNDATION, MATURATION, AND FERTILISATION. 320 
place, Phallusia agrees with all the other forms in the ovocyte I, 
containing half the number of chromosomes typical for the 
given species. Riickert (6) puts this first and foremost among 
the few ascertained facts that we have at present in this com- 
plicated subject. He writes: —‘‘ Alle genauere Untersuchungen 
der letzen Jahre stimmen darin ueberein, dass schon vor der 
ersten Reifungstheilung Chromatin-portionem auftreten deren 
Zahl die Hilfte betriigt von der Normalzahl der Chromosomen 
der betreffenden Species. ... Am klarsten liegt der Rei- 
fungsvorgang, wenn sie aus vier deutlich geschiedenen Unter- 
abtheilungen, Stabchen oder Kugeln, bestehen ( Vierergruppen). 
In diesem typischen Fall geht die Reifung bekanntlich folgen- 
dermassen vor sich: Durch zwei ohne Ruhephase auf einander 
folgende mitotische Reifungstheilungen werden die Vierer- 
gruppen in der Weise gevierteilt dass in jede Enkelzelle 
(Spermatiden, Reifes Ei) von jeder Gruppe ein einziges 
Stabchen als Chromosoma gelangt, womit die schon durch 
die Zahl der Vierergruppen vorbereitete Reduktion definitiv 
vollzogen wird.” 
It is obvious that if these “ Vierergruppen” are to be looked 
for in Phallusia, it is not in the nucleus of the ovocyte I-that 
they are contained, but in the three polar bodies and the female 
pronucleus. That is to say, there are eight ‘‘ Vierergruppen,”’ 
as each of the eight chromosomes divides twice, making thirty- 
two pieces in all. Julin, on the other hand, looks upon the 
eight chromosomes in Styelopsis as themselves forming two 
“‘ Vierergruppen;” and the subsequent formation of the polar 
bodies, albeit on these he confesses to have made few observa- 
tions, bears out this view. At the first polar division four 
chromosomes pass out, and at the second two, leaving two 
quarters of the two original chromosomes, which had divided 
twice precociously to give rise to two ‘‘ Vierergruppen.” The 
spermatozoon brings into the ovum two quarters likewise, so 
that the first segmentation nucleus possesses four chromosomes, 
or double the number contained in the nucleus of the ovocyte I. 
In fact, as regards the number of chromosomes, Styelopsis 
exactly resembles Ascaris bivaleus. In Phallusia each of 
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