30 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
reticulum, beiug, as it were, a gathering up of its strands; or, to put it 
in another way, nerves are a special development of the reticulum along 
certain lines. These special developments are generally marked by an 
increase in the number of nuclei, such increase being particularly great 
in the neighbourhood of the ganglion. The development of nerves is 
not an outgrowth of cell-processes from certain central cells, but is a 
differentiation of a substance which was already in position ; this differ- 
entiation seems to take place from the medullary walls outwards to the 
periphery, both in the anterior and the posterior roots, and to precede, 
or to proceed j oari passu with, the development of other tissue. The 
nerve-crest, then, is a centre for the growth of nuclei ; there are many 
other such centres, as the walls of the coelom, the caudal swellings, and, 
in the Amniota, the primitive streak. All these centres of growth are 
in so-called epithelial tissues, of which, indeed, at one stage many 
embryos are entirely composed. 
Mr. Sedgwick adduces evidence to show that nervous, muscular, con- 
nective, and vascular tissues are all developed in continuity, and proceeds 
to discuss some details of the development of the cranial nerves of 
Elasmobranchs, into which our space will not allow us to follow him. 
"We must be content to report that the embryonic medullary wall is con- 
nected with the reticulum by pale fibres similar to those which compose 
the reticulum, and the nerve-roots, both anterior, posterior, and cranial, 
are special enlargements of such connecting strands. “ They are formed 
at a time when no structures which could be called cells by any but a 
fanatical devotee of the cellular theory are present.” 
This essay will probably give rise to a lively discussion. 
Experimental Embryology.* — Dr. E. Zoja has experimented with 
ova of Clytia flavidula, Laodice cruciata , Mitrocoma Annse , Liriope 
mucronata , Geryonia proboscidalis, and other Medusae, isolating blasto- 
meres by operation. He finds that a fraction as small as 1/16 will 
follow a development like that of the entire ovum and will produce an 
entire organism. The limit observed by Driesch and Wilson in Echinoid 
and Amphioxus ova was one-quarter. There is nothing about the deve- 
lopment of the Medusoid blastomeres to suggest indirect regenerative 
processes, each segment developes like the whole ovum. The facts 
point to the conclusion that the early cleavages are quantitative. 
Human Embryology, f — Dr. W. 0. Manton has published a syllabus 
of lectures on Human Embryology, as an introduction to the study of 
Obstetrics and Gynaecology. The work is certainly not adapted for the 
general student ; the “ numerous outline drawings ” have a very sketchy 
appearance, and are not well executed. 
Development of Primordial Cranium in Man.f — Herr M. Jacoby 
comes to the following general conclusions : — First, as to the method of 
development, it is inaccurate to adopt Kolliker’s generalization according 
to which the cranium ceases at an early stage to differentiate, and only 
grows. Although it is indeed a continuous mass -without separate carti- 
lages, there are distinct parts and histological hints of progressive dif- 
* Anat. Anzeig., v. (1894) pp. 195-8. 
t Philadelphia and London, 8vo, 1894, vi. and 125 pp., 69 fgs. 
X Arch. f. Mikr. Anat., xliv. (1894) pp. 61-86 (1 pi.). 
