459 
SUMMARY 
OP CURRENT RESEARCHES RELATING TO 
ZOOLOGY AND BOTANY 
{'principally Invertebrata and Crypto gamia), 
MICROSCOPY, Ac., 
INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS. 
ZOOLOGY. 
A. VERTEBRATA: — Embryology, Histology, and General. 
a. Embryology. f 
Parthenogenetic Segmentation of Ova of Mammals .{ — M. L. F. 
Henneguy’s observations on the degeneration of the ova of Mammals 
confirm and extend those of Flemming and Schottlander. They show 
that the ovule in follicles that are undergoing atresia may present not 
only a precocious maturity, as evidenced by the appearance of a directive 
spindle and a polar globule, but also a commencing, irregular, partheno- 
genetic segmentation. They further show that the chromatic substance 
of the nucleus, when dispersed in the cytoplasm, continues to exercise an 
action on it. In the absence of centrosomes the chromosomes become 
centres of attraction and orientation for the achromatic filaments. 
Origin of Mesoderm.§ — Dr. J. Perenyi gives the following account 
of the origin of the mesoderm in the frog. In the blastula the dark pole 
consists of three layers of cells. These curve inwards at the equatorial 
margin at one side, and a unilateral epibole results. This epibole begins 
in the form of an angle with a right and a left margin, i. e. the duplica- 
tion takes place in two portions. Subsequently, in the position defined by 
the two margins, there arises the primitive streak, the basis of the medul- 
lary groove. The original orientation of the egg changes ; the dorsal part 
of the embryo appears at one side of the white pole, the ventral part on 
the dark pole. The originally outermost layer of ingrowing cells extends 
first vertically and forms the notochord, then horizontally, to right and 
* 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. 
t This section includes not only papers relating to Embryology properly so called, 
but also those dealing with Evolution, Development, and Reproduction, and allied 
subjects. J Comptes Rendus, cxvi. (1893) pp. 1157-9. 
§ Math. Nat. Ber. Ungarn, viii. (1891) pp. 272-8 (2 pis.); Math. Termes. Ertes. 
(Math. Nat. Anzeig. Akad.), viii. pp. 11-9. 
1893. 2 K 
