212 
Katharine Foot and E. C. Strobell 
que c’est un element unique, un monosome, et que son partenaire 
fait defaut. Quant ä la division longitudinale precoce, eile est en rapport 
aussi avec ce qivon a constate chez les heterochromosomes decrits. . . . 
No\is devons avouer que cet element que nous decrivons pour la pre- 
miere fois chez le chat, offre une singuliere ressemblance avec l’hetero- 
chromosome des insectes. Evidemment il faudrait, pour conclure avec 
certitude, l’avoir suivi pendant la maturation ainsi que pendant les mi- 
toses somatiques. Dans ces dernieres, nous avons retrouve frequemment 
un chromosome plus grand que les autres, mais les mitoses sont moins 
accessibles ä Fanalvse. Quant aux noyaux somatiques au repos, F element 
y est tout aussi invisible que dans les oogonies (noyaux protobroques). 
Quoi qu'il en soit, nous pensons qu'il y a de fortes presomptions en 
faveur de l’hypothese qu’un element, analogue ä Fheterochromosome, 
existe chez les chats, et peut-etre chez tous les mammiferes. » 
It will be seen that the behavior of the chromatin nucleolus in the 
ovary of the cat agrees with Buchner’s and Gutherz’s observations 
on the ovary of Gryllus on one important point. All four authors find 
the structure behaving as a single body in mitosis though they differ 
as to its method of division. Büchner finds it passing undivided to one 
daughter cell whereas Gutherz and Winiwater and Sainmont find it 
is divided equally between the daughter cells, though the last two authors 
find it most frequently lagging in division. 
We have never found this body appearing as a chromatin nucleolus 
dirring mitosis. On the contrary, we find evidencc that the two large 
chromosomes are evolved from the chromatin nucleolus. This is shown in 
photo 56 and the evidence in detail is given on page 000. This woidd 
indicate that the chromatin nucleolus in the ovary of Protenor does not 
persist as such througli mitosis and therefore does not divide as a single 
body. But on the other hand we find pseudo-reduced groups of chromo- 
somes not only in zone C of the terminal chamber but in zones B and A 
and in these cases the large chromosomes would presumably divide as 
a single body. 
We have however been unable to discover any evidence of the diffe- 
rential mitoses described by Giardina in Dytiscus (1901) and supported by 
Debaisieux (1909) and Günthert (1910). The ring of Dytiscus which 
these four differential mitoses finallv consign to one cell in a group of 
sixteen has little in common with the ovarian nucleolus of Protenor. Their 
morphological dissimilarity is evident if we compare the ring figured 
by these three authors with our photographs of the chromatin nucleolus 
in plates XIV— XVII. 
