ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
323 
Tlie author is, further, of opiniou that different mammals may have 
ostia tuboe which are not homologous ; in the Mouse and the Rabbit the 
ostium is found in a different part of the Wolffian body from that of 
Insectivora. In the Mouse the vertical piece of the Mullerian duct is 
laid down at the same time as the ostium of Insectivora, while the 
definite ostium of the mouse is formed much later, and only acquires a 
secondary connection with the vertical piece of the duct. The Mullerian 
duct of the Mouse arises from a rudimentary ostium, which must be 
homologized with the ostium of the Insectivora. In the Rabbit there is 
a rudimentary ostium which is doubtless homologous with that of In- 
sectivora, while the definite ostium does not appear till later, and then 
at quite a different place. 
Development of Thymus, Thyroid, and Carotid Glands.* — M. A. 
Prenant finds that the carotid is a blood- vascular gland, that is to say, 
it is an epithelial organ penetrated by vessels, which, like the head of 
the thymus, arise at the expense of the third endodermic branchial pouch. 
The author’s observations on the thymus confirm essentially the facts 
stated by Kolliker, de Tourneux, and Herrmann for the histogenesis of 
this gland, those of Flemming for the histological arrangement of the 
parenchyma, and those of Hansemann for the cytogenesis of the elements 
of the thymus. In sheep-embryos of 85 mm. or more, the thymus be- 
comes differentiated into a cortical mass and a medullary substance, the 
latter being clearer, of looser texture, and much poorer in lymphatic 
elements. In the cortical substance a peripheral zone becomes differen- 
tiated, and is, without doubt, a proliferating zone, for there are to be 
seen in it mitotic figures which are wanting in the rest of the cortical 
substance. It is probable that the epithelial cells, after having multi- 
plied actively by kinesis, give rise to lymphoblasts, either by kinesis or 
by nuclear stenosis. In the latter case small nuclear buds may be 
observed to be produced, and small nuclei may be seen near larger 
nuclei, or even in the same cell. It is probable that a certain number 
of epithelial cells persist in the completely developed organ under the 
form of supporting cells ; these may be compared, both in destiny and 
form, as well as by the constitution of their nucleus, to the supporting 
cells of the testicle, while the masses of lymphocytes would be com- 
parable to the seminal elements. 
Summing up his results as to the thyroid gland, the author remarks 
that the fourth endodermic branchial pouch is formed of two branches, 
the inner of which is prolonged and dilated into a pyriform vesicle. In 
the angle of the two branches there is formed, by the thickening of the 
epithelial wall of the pouch, a body which may be called the thyroid 
gland. By its trabeculated and reticulated structure, by the histological 
character of its epithelial elements, and because of its great and pre- 
cocious vascularity, and above all by its mode of formation, this body is 
comparable to the carotid gland. It has nothing in common with the 
thymus. In the course of development a cavity appears, the wall of 
which is formed by an epithelium that is at first stratified, and after- 
wards simple ; around it is produced a dense tissue of cellular and 
reticulated appearance, which disappears later on. 
Z 2 
La Cellule, x. (1894) pp. 87-184 (4 pis.). 
