ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
607 
There are two kinds of “ monophyodontism ” in Mammals. In the 
lower forms it is due to a non-appearance of the second set ; in the 
higher forms it is due to a suppression of the first set. In higher 
Mammals the monophyodont state is always the result of regression, but 
this is not the case in Marsupials at least. It seems likely that the 
second set has been gradually acquired by the Mammals. Prof. Leche 
closes with a discussion of the differentiation of the various types of 
dentition. His detailed memoir will be looked for with expectation. 
Development of Urino-genital System in Birds.* — Prof. C. K. 
Hoffmann has investigated this in various Grallatores and Natatores 
( Totanus , Vanellus, Larus , Sterna , Tringa , Fulica , &c.), whose embryos 
are preferable to those of the fowl. All the embryos were taken from the 
nest, the abnormalities of artificial incubation being thereby avoided. 
In the present memoir the author deals with the development of the 
gonads, the supra-renal capsules, and the oviducts. As to the kidneys, 
he has not yet obtained satisfactory results. 
As is well known, the gonads, at first in a sexually indifferent state, 
develope from a patch of germinal epithelium on the wall of the abdo- 
minal cavity. At the expense of the lateral germinal epithelium, the 
Mullerian duct developes ; the median part forms the gonads with its 
large “ primitive ovules.” These are present in very early stages, e. g. 
in embryos with thirty-two somites, among the peritoneal cells. In 
fact, it seems impossible to state when they originate. They are not 
“privileged ” peritoneal cells at all events. The origin of the “ cordons 
genitaux ” from the Malpighian corpuscles , and their subsequent relation 
to the genital epithelium are described. 
In Grallatores and Natatores the right gonad developes for a con- 
siderable time as strongly as does the left. The Mullerian duct is at first 
equally developed in both sexes. Thus it is very difficult to distinguish 
at an early state embryo males from embryo females ; subsequently it 
becomes easier by the reduction of the genital “ cordons ” in the female. 
The history of these “ cordons ” in both sexes is described in detail. 
That each individual is originally hermaphrodite is more clear than ever. 
The author then describes the origin of the supra-renal capsules 
from nerve-strands of the sympathetic and renal strands from the 
Malpighian corpuscles of the Wolffian body. The Mullerian duct is 
formed quite independently of the Wolffian duct ; it begins as an 
invagination of peritoneal cells, but grows on its own account. 
Gastrulation in Chelonia.t — Prof. K. Mitsukuri has studied the 
process of gastrulation in Chelone caouana, and publishes a preliminary 
notice of his results. Over the great part of the blastoderm there is a 
separation into a superficial epiblast of columnar cells, and a lower com- 
posed of irregular stellate cells, and probably not forming a complete 
membrane. At the posterior end there is a small area in which this 
separation does not take place, and there is then a thick knob consisting 
of a reticulated mass of cells in the formation of which the subjacent 
yolk takes part ; this is the primitive plate or primitive knob. In the 
middle of this knob an invagination appears, which is the archenteron, 
* Verh. K. Akad. Wet. Ainstel., 1892, 54 pp. (7 pis.). 
t_Anat. Anzeig., viii. (1893) pp. 427-31 (8 figs.). 
