. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MORPHOLOGY OF SALAMANDER THYROID GLAND. 155 almost complete continuity of the epithelium and lack of colloid. It is therefore certain that it was not a peculiar thyroid structure characteristic for the offspring of one particular female. It may be said, then, that although as a rule the follicular pattern of the thyroid of A, maculatum does not show any striking changes corresponding to certain functional changes, such changes may develop in rare cases. They resemble the changes taking place regularly in A. opacum. It should
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MORPHOLOGY OF SALAMANDER THYROID GLAND. 155 almost complete continuity of the epithelium and lack of colloid. It is therefore certain that it was not a peculiar thyroid structure characteristic for the offspring of one particular female. It may be said, then, that although as a rule the follicular pattern of the thyroid of A, maculatum does not show any striking changes corresponding to certain functional changes, such changes may develop in rare cases. They resemble the changes taking place regularly in A. opacum. It should be noted especially that while the development of one particularly large tube-like follicle is not an integral phase in the functional cycle of the thyroid of the spotted salamander, it does occur occasionally. On the whole the differences of the follicular pattern of the thyroid, existing between two so closely related species as A. maculatum and A. opacum, are very striking. Yet the occurrence of the two exceptional cases of follicular pattern in A. maculatum shows, that in the thyroid of this species the ability of developing the follicular pattern of A. opacum is potentially present. Comparison of the thyroids of the two species of salamanders examined furnishes, we believe, further evidence to show that the plasticity of the endocrine system is very considerable in the group of amphibians. VARIABILITY OF THE NUMBER OF FOLLICLES. Owing to the extreme variability of the number of follicles it is difficult to determine whether or not a change in the number of follicles can be effected by any particular experimental pro- cedure. Nevertheless, as we have seen in experiments to be described in a subsequent paper (13), it is possible to change so considerably the number of follicles, that the degree of the change exceeds the degree of variability. In the present article we will discuss only such variations the causes of which are not entirely understood. As was pointed out, when
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
