ment of the Kidney, and the Development of the - Journal of Cell ...

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464 PETER GRAY D. DEVELOPMENT OF THE SEMINAL VESICLES. (i) Historical Note. No work appears to have been carried out upon the development of the seminal vesicle. Both Gerhartz (1905) and Nussbaum (1912) studied the seasonal variation, the former from the physiological and the latter from the histological aspect. They both agree—as was, indeed, well known before them—that the adult vesicle is composed of many coiled tubes, but they offer no suggestion as to the origin. Gerhartz, throughout his paper, treats the seminal vesicles of Eana as homologous with the vas deferens of Triton, which also shows a seasonal variation. This view is untenable as the sperm-duct in Triton is quite definitely the remains of the archinephric duct, the appendages to this duct being true ureters, both in function and origin (Gray, 1932). The view that the seminal vesicle of E a n a is homologous with the ureters of Triton is very attractive, since a morphological examination of the adult condition shows many points of resemblance. A study of the embryology, however, has convinced the writer that some other explanation must be sought and this explanation is put forward after the description which follows. (ii) Description. The first trace of the seminal vesicles may be found in a fourlegged tadpole. In this stage each of the archinephric ducts, when it leaves the kidney, passes ventrad along its own mesentery to enter the rectum. The general appearance is similar to the condition in Triton which was shown in Text-fig. 6, B, of Part II (Gray, 1932) of this investigation. In Rana, however, the mesentery is greatly expanded by large numbers of mesenchyme cells (a, fig.26, PI. 23) amongst which there lie from four to six agglomerations of kidney blastema (rsvt.). These agglomerations exactly resemble the capsuloblast vesicles which are still being formed in the kidney proper. Each of these rudiments acquires a connexion with the archinephric duct shortly after metamorphosis, but undergoes no alteration at the end farthest from the duct.
DEVELOPMENT OF AMPHIBIAN KIDNEY 465 During the course of the year following metamorphosis (fig. 25, PI. 23) these rudiments elongate into short tubules, lying parallel with the archinephric duct and become furnished with lumina. There is, as yet, no branching or coiling, and this is well shown in the figure where one duct is seen sectioned through about the middle of its length, while the other is cut through its blind tip. The mesenchyme has developed into the plentiful connective tissue of which the greater part of the organ is formed. During the second year (fig. 24, PI. 23) there is none of the branching and coiling which will be required to increase the storage capacity of these tubules, but there is a considerable increase in the size compared to the length. This figure has been selected to parallel fig. 25, PI. 23, as nearly as possible. It is during the third year (fig. 23, PL 23) that the branchings and coiling typical of the adult make their appearance. Each tubule not only sends out numerous branches but also coils and twists round the other tubules. Nussbaum's description of the histology of the adult seminal vesicle during resting period so thoroughly agrees with the appearance at this stage that no useful purpose would be served by a repetition. (iii) Possible Homologies. The suggestion that the seminal vesicles of E a n a are homologous with the ureters of Triton breaks down both on functional and embryological grounds. It has been shown (Gray, 1932) that the use of the word 'ureters' as applied to the excretory ducts of Triton is justifiable, as they are outgrowths of the archinephric duct. The seminal vesicles of Eana are derived from separate blastema masses and owe nothing of the material from which they are formed to the archinephric duct. Two other hypotheses must therefore be considered. Either the vesicles are peculiar to Anura and were evolved independently in response to a functional necessity: or they may represent some of the ancestral kidney specialized to the function of sperm-storage. The present writer accepts the latter hypothesis in preference to the former, and it is not difficult to find a homology which would justify this acceptance.
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