SUMMARY OF CURRENT RESEARCHES 
RELATING TO 
ZOOLOGY AND BOTANY 
(principally invertebrata and cryptogamia), 
MICEOSCOPY, Etc. 
Including Original Communications from Fellows and Others .* 
ZOOLOGY. 
VERTEBRATA Embryology, Histology, and General, 
a. Embryology* t 
Inadequacy of Cellular Theory of Development.f — Mr. A. Sedg- 
wick returns to the attack on the cellular theory which he made, in 
guarded terms, ten years ago. Notwithstanding changes of opinion 
among some biologists, Mr. Sedgwick finds that the theory still blinds 
men’s eyes to the most patent facts, and still obstructs the way of real 
progress in the knowledge of structure. One difficulty is that there is a 
want of precision about the cell-phantom which he desires to lay. 
To illustrate his meaning, Mr. Sedgwick first discusses the so-called 
mesenchyme tissue of Elasmobranch embryos ; this is said to consist of 
branched cells lying between the ectoderm and endoderm, but, as a 
matter of fact, there are no such separate cells, but in their place a 
reticulum of a pale non-staining substance, which holds nuclei at its 
nodes. Another erroneous view is that this tissue is not continuous with 
the ectoderm or endoderm, whereas the fact is that the primary layers 
are simply parts of this reticulum, in which the meshes are closer and 
the nuclei more numerous and arranged in layers. These facts can be 
easily seen, and they would, Mr. Sedgwick thinks, have been recognized 
long ago had it not been for the dominating influence of the cellular 
theory of development. Turning next to the origin of nerve-trunks and 
the fate of the neural crest, the nerves, he says, are developments of 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. 
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- X Quart. Journ. Micr. Sci., xxxvii. (1891) pp. 87-101. 
