324 
Dl L. SOÓS 
in ovogenesis). Popoff emphasizes that the resemblance in ovogenesis 
of Mammals and Paludina is so great that it extends even to details. 
As these observations show, an intercalated resting period in the 
development of the ovocytes is not rarely to be found during which 
the earlier formed chromosomes become dissolved, and even disappear, 
as Carnoy and Lebrun observed in the ovocytes of Amphibia. The 
matter is otherwise, as a rule, in spermatocytes. In the liteiature known 
by the present author only one contribution is to be found, according to 
which the chromosomes of the spermatocytes in a certain period disappear 
and the nucleus becomes a «resting» one [ Notodromas monacha , 
ScHLEiP (107)]. Popoff (94) put the question what circumstances cause 
the resemblance in ovogenesis of Mammals and Paludina ? This ques¬ 
tion also interests us, because not only is the ovogenesis of Mammals 
very similar to that of Paludina, but also the behavior of the sper¬ 
matocytes of Ii. arbustorum agrees in some respects with that of the 
ovocytes of the animals mentioned. Popoff refers to the similarity in 
the development of the eggs which is a result of the viviparism. The 
ova of the viviparous animals ripen at large intervals, for instance 
Paludina produces one egg a week. The ovocytes in the second part 
of the growth period form a constant stock from which from time to 
time one ripens, therefore their resting stage is easily to be understood. 
This explanation is not applicable to H. arbustorum, since the 
spermatocytes do not stay for a longer time within the genital gland like 
the ova of Paludina, or of the Mammals. I claim as explanation the 
fact referred to formerly by Woltereck (128), and recently by E. Hert- 
wig (49), according to which the cell prepares in the first part of the 
growth period for ^division. The preparing for division is shown by the 
phenomena of the transformations of the chromatin, in the forming of 
definite chromosomes and their splitting. The division, however, does 
not take place, i. e. we have to do with a division suppressed by some 
cause, but it is followed, according to the rules of the division, by a 
«resting stage». 
I believe that this suppressed division may be explained upon 
the base of the theory of the nucleo-plasmic ratio of R. Hertwig, upon 
which also Popoff (94) explained the suppressed divisions in ovogenesis 
of Paludina . The spermatogonia may be compared to the Protozoa 
cells the depressions of which become balanced by frequent divisions, 
but the energy of the cells after the last spermatogonial division be¬ 
comes exhausted so much in the struggling against the preceding de¬ 
pressions, i. e. the depression becomes so strong that a single division 
is no more sufficient to balance it, and division cannot be completed. 
