MR. E. C. BABER OR THE STRUCTURE OF THE THYROID GLAND. 
599 
liarities :—The capillaries, as usual, form a network running between the individual 
gland-vesicles, but in proportion to the size of the vesicles they do not appear so 
minute or to have such complicated ramifications as in the case of other animals 
(e.g., Sheep or Tortoise), but resemble more in their distribution the lymphatics in 
some of the Mammalia (see Plate G9, fig. I 7). The veins frequently surround either 
partially or entirely the arteries which they accompany (see Plate G9, fig. 18). Imme¬ 
diately under the surface of the capsule numerous large veins are seen, and in the 
fibrous capsule itself layers of red blood-corpuscles have been observed, which appear 
to be contained in blood-vessels communicating' with the veins in the interior. 
In a preliminary communication presented to the Society on this subject (Proc. 
Royal Society, No. 185, 1878), I mentioned that once or twice I had noticed in the 
large veins on the surface of the gland (under the capsule) in addition to red blood- 
corpuscles, and perhaps coloured injection, a greater or less quantity of a material of 
homogeneous aspect, presenting an appearance similar to the material seen in the 
vesicles, also to that described above in the lymphatics of the Dog. I do not, however, 
attach any importance to this, as the contents of the blood-vessels in the Dog, when 
coagulated, also sometimes present this homogeneous aspect. 
In the thyroid gland of the Rook no system of lymphatics becomes injected by the 
method of puncture, but the blood-vessels, presenting an appearance very similar to 
those in the Pigeon, become filled. 
Reptilia. — In the thyroid gland of the Tortoise a network of lymphatics can be 
injected by the method of puncture, of which the smaller ramifications run between 
almost all individual vesicles. In specimens injected with nitrate of silver the 
lymphatics are seen to be lined by a layer of endothelium, of which the cells are 
usually elongated and have a sinuous outline. The areas, stained dark with nitrate 
of silver (as described by Zeiss ; see above, p. 595), are well seen in this animal (see 
Plate 69, fig. 16). They vary much in size and shape, and often appear to have a 
double contour. Usually, though not always, they are situate on the boundary line 
separating two endothelial cells. In the Tortoise the lymphatics have not usually any 
visible contents, but they sometimes contain a granular material which stains scarcely 
at all with hematoxylin. 
Pisces .—In the thyroid gland of both Skate and Conger Eel an extensive system of 
vessels lined with endothelium becomes injected by the method of puncture. (A con¬ 
siderable portion of the injection, however, also passes into the meshes of the con¬ 
nective-tissue.) Being doubtful as to whether the vessels thus injected were of 
lymphatic or blood-vascular character, I injected the thyroid gland of a large Conger 
Eel with solution of Berlin blue from the blood-vessels (dorsal aorta and efferent 
branchial trunks); and from a comparison of the vessels injected in this case with 
those filled on injection by the puncture-method, I have been led to the conclusion 
that in the thyroid gland of the Conger Eel at least, as far as my observations extend, 
there is no evidence of any system of lymphatic vessels. Large veins, filled with red 
