SUMMARY OF CURRENT RESEARCHES 
RELATING TO 
ZOOLOGY AND BOTANY 
(principally invertebrata and cryptogamia), 
MICBOSCOPY, Etc. 
Including Original Communications from Fellows and Others .* 
ZOOLOGY. 
A. VERTEBRAT A Embryology, Histology, and General. 
a. Embryology. f 
Experimental Embryology. J — Prof. 0. Hertwig gives an elaborate 
account of bis experiments and observations on Amphibian ova, made 
with the view of determining the role of the various segmentation cells 
in forming the organs of the embryo, and of deciding for or against 
Roux’s mosaic theory of development. 
By various compressions and modifications of the ovum’s shape the 
course of segmentation, the direction and succession of the cleavage 
planes, and the size of the blastomeres are profoundly modified. The 
direction of the cleavage planes is always determined by the form and 
disposition of the cytoplasm. The position of the median plane of the 
embryo is not determined by the position of the first or second cleavage 
plane. In the various modifications of segmentation the nuclei, accom- 
panied by portions of the yolk, are disposed in the most diverse fashion, 
“ like a heap of balls thrown together.” Qualitatively different portions 
of the segmentation nucleus are not separated in the segmentation ; 
Weismann and Roux are wrong ; in spite of the disordered distribution 
of the nuclear material normal embryos always arise. The ovum is 
certainly differentiated, e. g. into formative protoplasm and yolk, but it 
is “ isotropic,” i. e. it is not made up of predetermined organ-forming 
areas or specialized substances definitely arranged. Gravity has a 
directive influence in determining the distribution of material and the 
* The Society are not intended to be denoted by the editorial “ we,” and they do 
not hold themselves responsible for the views of the authors of the papers noted, 
nor for any claim to novelty or otherwise made by them. The object of this part of 
the Journal is to present a summary of the papers as actually published , and to 
describe and illustrate Instruments, Apparatus, &c., which are either new or have 
not been previously described in this country. 
f This section includes not only papers relating to Embryology properly so called, 
but also those dealing with Evolution, Development and Reproduction, and allied 
subjects. X Arch. f. Mikr. Anat., xlii. (1893) pp. 662-807 (6 pis.). 
N 2 
