ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
51 
thinks also that Hertwig should allow something for the natural enthu- 
siasm of the discoverers of a new and fruitful method in biology. 
The paper also includes a brief account of the reply which Roux 
himself makes to Hertwig. The aim of the new school, according to 
him, is to refer the phenomena of the organic world to the fewest possible 
causes ( WirJcungsweisen ), and to explain each particular phenomenon as 
the result of a special combination of these general causes. In reply to 
Hertwig’s attack upon the experimental method in embryology, he admits 
that the method can only yield fruitful results when combined with other 
methods, but protests against Hertwig’s dismissal of the results as 
“ pathological.” The changes produced are quantitative, and not quali- 
tative ; they have their homologues in the so-called “ normal ” organism, 
and must therefore be of value in the comprehension of these normal 
processes. 
Albrecht’s summing up is in favour of Roux; but he so far agrees 
with Hertwig that he believes that the terms used by Roux are liable to 
misconception, even if Roux himself has not been guilty of a misuse of 
them. He strongly pleads, therefore, for a revisal of nomenclature, and 
deprecates the rash use of terms like “ formative forces ” ( gestaltendc 
Krafte) by a school which has already made good its claim to rank with 
the existing schools of morphologists and physiologists. 
Gastrulation in Amphioxus.* — Hr. J. Sobotta has worked through 
the early stages of the development in Amphioxas , in order to decide 
the question at issue between Hatschek and Lwoff. Lwoff dissents from 
Hatschek’s well-known description in that he believes that the micro- 
meres of the blastospliere form part of the endoderm as well as the whole 
of the ectoderm. He believes that certain of the small cells are the 
active agents in the process of invagination, and that they form the roof 
of the mid-gut. Sobotta’s results confirm those of Hatschek in almost 
all particulars, but in two points they support Lwoff. The two points 
relate to the method of closure of the blastopore, and the so-called 
pole-cells of the mesoderm. Sobotta denies that the blastopore becomes 
slit-like and closes from before backwards. He believes that it gradually 
diminishes on all sides. He was further quite unable to find the pole- 
cells, and believes that they do not exist, certainly not, at least, in those 
early stages in v/hich they were described by Hatschek. 
Gastrulation in Vertebrates.']* — Dr. J. Sobotta discusses briefly the 
discogastrula of Selachii and Teleostei, the amphigastrula of Amphibia, 
the epigastrula of Amniota, and the primitive archigastrula of the 
lancelet. 
Development of Rodent Dentition. i — Herr P. Adloff has studied the 
embryos of a number of Rodents, and has got some interesting results, 
of which the most important seems to be that the minute rudiments of 
front teeth, repeatedly described, are not the deciduous representatives 
of the large gnawing teeth, but correspond to a more anterior pair of 
incisors — the first incisors in other forms. The large gnawing teeth are 
really the second incisors. 
* Verhandl. Phys.-Med. Ges. Wiirzbuvg, xxxi. (1837) pp. 1-21 (1 pi. and 20 figs.). 
t SB. Phys.-Med. Ges. Wurzburg, 1897, p. 9. 
% Zool. Auzeig., xx. (1897) pp. 32-1-9. 
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