ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
449 
through the glandular epithelium, to the chorionic epithelium close to 
which they accumulate. At a later stage, the tissue between the more 
numerous villi is much reduced ; the villi are separated by thin strands 
each with a capillary close to which the chorionic epithelium lies. The 
villi eventually insinuate themselves into the glandular spaces, and 
their epithelial cells are modified for the absorption of the “ uterine 
milk” — the secretion and debris of the glands. Outside the strict 
placenta, red blood-corpuscles have accumulated around the chorionic 
epithelium, by which they are absorbed and probably utilized. 
Gastrulation in Lacerta agilis.* — Dr. K. F. Wenckebach finds that 
the bilaminate stage of the germinal disc of Lacerta is due to cleavage 
and not to invagination. Gastrulation is effected by the invagination of 
the upper layer ; only a small part of the enteric wall is formed from 
the archenteron ; the notochord is formed in its dorsal wall, and with 
this is developed the gastric mesoderm ; the peristomial mesoderm is 
developed from the whole circumference of the blastopore. The forma- 
tion of the notochord and gastric mesoderm is continued towards the 
cranium in the lower layer. The author points out the resemblance 
between the gastrulation of the Reptilian egg and that of the 
Mammalia. While the egg of Amphioxus may be called the primary 
holoblastic egg, that of Amphibians is secondary, and that of Mammals 
tertiary. The recent work of L. Will on the development of the Gecko 
would make it, if taken in combination with the author’s observations on 
the Lizard, possible to derive the gastrula of Mammals from that of 
Amphibians even without the assistance given by Ichthyophis and Echidna . 
Foetal Membranes in Chelonia.f — Prof. K. Mitsukuri has pub- 
lished in detail and with illustrations an account of his studies on the 
foetal membranes of Chelonia, the preliminary notice of which has 
already been reported.^ It will be remembered that he called attention 
to the presence of a rudimentary placenta, and he now makes some 
suggestions as to the phylogeny of the foetal membranes in Vertebrates. 
He strongly inclines to the view that the amnion was originally 
developed by mechanical causes ; there are, in the Chelonia, two reasons 
why the headfold, when produced, should sink into the yolk below. 
The yolk is very large and liquid, so that a slight weight is sufficient to 
sink any structure into it, and there is no space for the headfold to grow 
in any other direction than downwards. It is the dorsal part of the 
proamnion that primarily consisted of epiblast only. 
Primitive Segmentation of Vertebrate Brain.§— Mr. B. H. Waters 
has made a study of the brain of Gadus morrhua, from which he con- 
cludes that the neuromeres appear at a late period in the ontogeny and 
soon degenerate ; this disproves the view that they are formed mechani- 
cally, and strengthens that of their phylogenetic importance. The 
olfactory pits develope early in connection with the first pair of nerves 
which arise from the fore-brain. This fore-brain contains three neuro- 
meres ; from the first the roots of the olfactory nerve arise ; and at a 
point somewhat above the second the optic diverticula are formed. The 
* Anat. Anzeig., vi. (1891) pp. 57-61, 72-7 (15 figs.). 
t Journ. College of Science, Imp. Univ. Japan, iv. (1891) pp. 1-53 (10 pis.). 
j See ante , p. 22. § Zool. Anzeig., xiv. (1891) pp. 141-4. 
