ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
35 
sion that two sets of calcified teeth are generally developed in Mammals 
of this order, and that it is characteristic of them to exhibit a tendency 
towards a reduction of the milk-set, with early development of the 
replacing dentition. 
Histogenesis of the Pancreas.* * * § — Dr. E. Laguesse has studied this 
in the sheep. On the primitive pancreatic diverticulum solid buds 
arise which ramify irregularly and form the primitive varicose strands. 
These anastomose, are hollowed by the formation and enlargement of 
intercellular cavities, and form the primitive pancreatic tubes. But 
still these exhibit solid anastomoses, which only gradually disappear. 
Besides the solid buds which form the first “ islets of Langerlians,” they 
give origin to numerous hollow buds, which enlarge, and become thinner 
in their walls. At the ends there are lobed vesicles, and along the 
tubes there are scattered elements, isolated or grouped, which may be 
regarded as the precursors of the true secretory cells. 
Development of Bladder and XJrinogenitai Sinus.t — Herr Keibel 
has followed the modelling method in a study of a series of human 
embryos, and has generally corroborated his previous conclusion that 
the bladder does not arise from the allantois or allantoic duct, but in 
part at least from the endodermic cloaca. The latter is divided by two 
lateral folds, forming a frontal partition, into the ventral bladder and 
urinogenital sinus, and a dorsal gut region. The details are, however, 
too complex for brief summary. 
The author also directs attention t to his models of pig embryos, 
which shed light on the closure of the medullary canal in the head 
region, the rudiments of the optic vesicles, the mouth, the visceral clefts, 
the auditory sac, and the first protovertebra. 
Embryology of Bats.§ — Prof. M. Duval has especially studied 
Vespertilio murinus. He has some interesting notes to make on their 
reproductive habits ; thus, for most European species, it seems now 
well established that copulation occurs before the winter, that the 
sperms remain throughout the winter stored up in the uterus, and that 
the development of the egg does not begin until the following spring 
after the animal awakens. In the great majority of cases ovulation 
and fertilisation occur in April ; in exceptional cases they seem to occur 
in winter. Moreover, young forms which were not mature in autumn, 
have been known to pair in spring. 
The uterus of the virgin female has two equal cornua ; in the mature 
animal the cornua dilate with a slight predominance of the right, after 
fecundation the uterus increases in volume and the right horn is more 
and more accented. It is in the right that the ovum is fixed. The 
changes in the form of the uterus are mainly due to the hypertrophy 
of the mucosa and its glands ; the uterine epithelium loses its cilia when 
the ovum descends, and as the latter becomes fixed the epithelium entirely 
disappears. 
Gestation is always (in 300 cases) in the right horn of the uterus, 
* Journ. de l’Anat. Physiol., xxxi. (1895) pp. 475-500 (19 figs.). 
t Verh. Anat. Ges., ix. (1895) in Anat. Anzeig. Erganzungslieft, x. (1895)^ 
pp. 189-99 (4 pis.). t Tom. cit , pp. 199-201. 
§ Journ. de l’Anat. Physiol., xxxi. (1895) pp. 93-160 (1 pi. and 9 figs.). 
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