584 
HR, E. C. BABER OH THE STRUCTURE OF THE THYROID GLAXD. 
obtained by flotation. Our observations also agree, inasmuch as Zeiss observed these 
tubes in the glands of young animals : at least be makes no statement to the effect 
that they have been found in the glands of adult animals. From the fact of their 
complete, or almost entire, absence in the glands of adult Dogs, I regard these much- 
branched vesicles merely a.s forming a stage in the growth of the organ, and consider 
that in its fully developed state the gland-vesicles form cavities more or less spherical 
in shape, which are very rarely, if at all, branched, or, in other words, in com¬ 
munication with one another. The presence of branched vesicles in a gland probably 
indicates that the number of vesicles is being increased by the growth into the vesicles 
already present of involutions of their walls, together with processes of the inter- 
vesicular tissue. Peremeschko ( loc. cit.) figures this division of the gland vesicles 
both in the embryo and adult Pmbbit. He considers it probable that the division of 
vesicles takes place after intra-uterine life. W. Muller is also of opinion, from an 
examination of the gland at different ages in Man, that completely-formed follicles 
(vesicles) undergo segmentation by the growth into them of processes of the mesoblast. 
I shall have occasion to refer to W. Muller’s observations on the early stage in the 
development of the gland in speaking of the “ undeveloped portions.” 
The above conclusions refer to the thyroid gland of the Dog, as it is in this animal 
that I have chiefly studied the shape of the vesicles. 
In the thyroid gland of Birds (Book, Fowl, Pigeon), as far as I have seen, the vesicles 
are, as a rule, small and very rarely branched. In the last-named bird (Pigeon) the 
larger vesicles are usually found near the surface of the gland. 
In the Tortoise the vesicles are sometimes, but not usually, branched. 
In the thyroid gland of full-sized Frogs the vesicles are usually large. In smaller 
Frogs their size is generally less. They are occasionally branched. 
The gland-vesicles of the Conger Eel are often of large size and more or less 
branched. In the Skate the vesicles are also often large, and branched ones are some¬ 
times seen. 
In all these animals the exact age was unascertained. 
Whilst, therefore, branched vesicles may occur in the thyroid gland of adult animals, 
they do not, as far as I have seen, communicate with one another to any extent—• 
a conclusion which, it appears to me, is strongly corroborated by the fact that in the 
course of a large number of interstitial injections in the glands of different animals 
I have never succeeded in injecting any system of branched tubes. I cannot think 
with Zetss that the viscid contents of the vesicles would have the effect of preventing 
the injecting fluid from entering them, when we know that the viscid contents of the 
lymphatics has no such effect. 
The exact shape of the vesicles is of course of minor importance. My chief object 
in drawing attention to this point has been to show that in the adult state the vesicles 
form closed cavities, and do not consist of a system of tubes traversing the substance 
of the gland as Bo ecu at suggests. 
