814 The American Naturalist. [September, 
is doubtless a germ of proliferation. Nothing surrounding the organ 
authorizes the supposition that this is a muscular connective tissue 
which produces the lymphocytes that fill the organ. It is probable 
that epithelial cells after multiplying actively by mitosis, give rise to 
the lymphocytes by simple division (stenose). For large nuclei with 
small buds frequently occur and small nuclear bodies may be seen by 
the side of large nuclei and within the same. This mode of division is 
more common in the earlier stages. In older embryos the lymphocytes 
are formed karyokinetically. The epithelial cells that probably persist 
even in the completely developed organ he compares with the cells 
forming the matrix of the testis and the coveys of lymphocytes aris- 
ing from them with the seminal elements. 
The lateral portions of the thyroid develop from the fourth entoder- 
mal branchial pouch, which is forked. From the angle of this there 
grows up an organ that in structure and appearance is comparable 
with the carotid gland. This he calls the glande thyroidienne. It 
finally comes to lie outside of the vascular-connective hilum of the thy- 
roid. During development an anfractuous cavity appears in the thyroid 
and is prolonged in every direction by deep diverticula. At first its walls 
are stratified and then simple. The superficial cells disappear after a 
transformation comparable to that which occurs in the internal assizes 
of the epithelium of the esophagus. The wall produces around itself a 
cellular reticulate structure of dense aspect, which later disappears. 
Whether the lateral gland gives rise to buds that become confusingly 
anastomosed and eventually transformed into thyroid vesicles, or 
whether the lobes of the median gland solder themselves to the tissue 
of the lateral gland, it is impossible to say. 
There is very little of a comparative nature in the paper beyond an 
attempt to introduce a formula to represent the number and position of 
the glands in invertebrata. This is not nearly as readily understood 
as a simple diagramatic figure; moreover, it is entirely unnecessary. 
Of possible interest in connection with the work of Prenant is a 
short paper by J. Beard on the Development and Probable Function 
ofthe Thymus? In Raja he declares that the epithelial nature and 
appearance of the cells composing the gland is lost very soon after their 
formation. Their nuclei stain intensely, and the cell-body, i. e., the 
protoplasm, is very scant from the start. It is clear that there is no in- 
wandering of lymph cells, but that these elements are the direct off- 
spring of the epithelium of the gill cleft. 
*Anat. Anz., IX, p. 476. 
Wis 
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