SUMMARY OF CURRENT RESEARCHES 
RELATING TO 
ZOOLOGY AND BOTANY 
(principally invertebrata and cryptogamia), 
MICROSCOPY, Etc. 
Including Original Communications from Fellows and Others * 
ZOOLOGY. 
YERTEBRATA Embryology, Histology, and General. 
a. Embryology, f 
Early Stages in the Development of Vertebrates.^ — Herr B. L wolf 
has a somewhat lengthy memoir on the formation of the primary germinal 
layers, and on the origin of the notochord and mesoderm in Vertebrata. 
His investigations have led him to conclusions which in many points 
contradict many embryological theories which are current to-day. He 
finds that the differentiation of the primary germinal layers is very 
various in various Vertebrates, and the history cannot be compressed 
into one general scheme. Thus, in Amphioxus , the smaller ectodermal 
cells can be distinguished from the larger endodermal cells in the 
blastula stage. The typical condition in the process of differentia- 
tion of the primary germinal layers in holoblastic eggs is this — that 
the endodermal elements are surrounded by the ectodermal elements ; 
but this final result may be obtained in various ways. In mero- 
blastic eggs, where the primitive conditions are altered, cleavage is 
effected on one side, and there is partial or unilateral delamination. In 
Amfhioxus the endoderm is formed by invagination, but in other Verte- 
brates there is no invagination at all. There may be epiboly, delamina- 
tion, or partial delamination. The foundations of the notochord and of 
the mesoderm are due partly to cleavage from the ectoderm, partly to 
the growing round of the ectodermal cells, which form a thickening. A 
typical condition in the development of Vertebrates is the formation of 
a continuous plate of cells, partly by infolding, and partly by cleavage 
* 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. X Bull. Soc. Imp. Moscou, 1894, pp. 57-137, 160-256 (6 pis.). 
