SUMMARY OF CURRENT RESEARCHES. 
493 
breaking clown when we come to consider the question of heredity. In 
the second volume, which is devoted to the mechanics of development, 
there are replies to the successive publications of Driesch and Hertwig. 
It is remarked that Prof. Roux has only himself to thank if more atten- 
tion is paid to the publications of these observers than to his work, for 
he, as has been said, has carried in this subject theorising and prolixity 
to an intolerable excess. 
Experimental Embryology.* — Herr Hs. Driesch answers some criti- 
cisms brought against the experiments made by him and by T, H. Morgan 
on the developing ova of Ctenophora. (1) Roux says that Chun reared 
the half-larvae to sexual maturity and then observed post-generation, 
while the fact is that Chun inferred post-generation from the appearance 
presented by certain Ctenopliore larvae which he captured. (2) Roux 
suggests that the third small pocket which Driesch and Morgan ob- 
served on most of the products of an isolated blastomere is a post-genera- 
tion phenomenon. But this is inconsistent with the fact that when 
pouches were clearly developed all the three on one side were equally 
so ; nor did the third pouch increase in any way during the next two 
days. (3) Roux declares that post-generation remains unknown to 
Driesch, who responds that the occurrence of post-generation remains- 
non-proven. He goes on to show that he is no “Neo-Darwinist,” that 
he is not prejudiced, that his conceptions of development are not domi- 
nated by any fundamental hypothesis, and so on. 
Herr G. Wetzel | discusses the meaning of the circular cleft in 
Schultze’s double forms of frog embryos. It is a rather intricate 
matter, but the conclusion come to is that the cleft is formed by the 
juxtaposition of two blastopore lips, and is itself neither blastopore nor 
primitive groove, but a consequence of the peculiar process of gastrula- 
tion. At the same time, so far as it goes, it divides the twin embryos 
from one another and represents their ideal plane of division. Herr 
Wetzel also concludes that the separation of the black material into two 
parts by the interposition of white substauce is the condition of the 
separate development of two individuals from one ovum, for it divides 
two areas of growth and cell-multiplication which differentiate separately. 
Fertilisation.}: — Prof. W. Schimkewitsch recognises in fertilisation 
the combination of two plasmas, two centrosomes, and two nuclei, all 
implying structural and functional conditions of great complexity. He 
compares the degeneration of rapidly dividing, non-conjugating Infu- 
soria, with the ageing of Metazoa, as also with the conditions of close 
inbreeding and autogamy. The necessary imperfection in each division 
of the nucleus implies trophic imperfections in the daughter-cells; as 
these mount up, old age sets in and death occurs. Cross-fertilisation is 
a counteractive of specific degeneration, but it cannot be more than 
approximate. Inbreeding and autogamy increase the risks. Examina- 
tion of the observations of Ryder and Pennington, on the conjugation of 
somatic cells in Porcellio, did not confirm them, but showed that the 
appearances described were artificial. 
* Zool. Anzeig., xix. (1896) pp. 127-32. 
t Arcli. f. Mikr. Anat., xlvi. (1895) pp. 651-73 (1 pi. aud 5 figs.). 
X Biol. Centralbl., xvi. (1896) pp. 177-81. 
