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

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466 PETER GRAY It has been shown (Gray, 1930) that there arise throughout the whole length of the kidney a series of early units which degenerate throughout the length of the functional kidney, except for a slightly later generation which persist as straight tubules. The present investigation has shown that these straight tubules are all that remain of the sexual kidney shown more clearly in Triton. Now there is a marked similarity between the development of the straight tubule units and the tubules of the seminal vesicle. Each starts as a capsuloblast vesicle, delayed both in its origin and development; each is primarily devoted to a sexual function. It seems reasonable to suppose that at one time the sexual units extended throughout the whole length of the kidney and that they have been retained only at the anterior and posterior ends, in which regions alone does there exist any need for a sexually specialized unit. The outstanding peculiarity in the development of the seminal vesicles is their origin from separate blastema condensations and not from the archinephric duct itself, which latter would be the normal thing to have happened in the course of a separate evolution. E. REVIEW. The facts brought forward in this paper do not justify a lengthy comparative discussion. Nothing is known about the post-metamorphic development of the kidney in any other amphibian, and the few fragmentary papers which have appeared on the later development of the kidneys in other groups offer no opportunities for comparison. The formation of the vasa efferentia, even though here fully described for the first time, shows no departure from what is already known for other groups of vertebrates. It has long been accepted that the testis-kidney connexion in birds and mammals is primitive, and not a secondary production of either organ. The discussion of the development of the frog's kidney is of more interest. It is now perfectly clear that the sexual and asexual kidneys in Amphibia are distinct from each other in origin and become intermingled only in course of development. The sexual kidney is represented by two sets of units, the
DEVELOPMENT OF AMPHIBIAN KIDNEY 467 interval between the appearance of each set being directly correlated with the functional need for their production. The first set, termed 'early units' in the writer's previous paper, develops rapidly to a functional condition as the pronephric method of excretion becomes insufficient for the tadpole's needs. The second set is modified at the extreme anterior and posterior ends to sexual function; in the middle region it secondarily acquires an excretory use, and develops more slowly. The functional kidney of the adult develops separately from units Avhich, since the excretory needs of the young animal are amply covered by the pronephros and early units, do not become directly or immediately attached to the archinephric duct. These units do not appear at all at the extreme anterior end. In the antero-middle region they become connected to the straight tubules, which here carry both sperm and excretory products; in the postero-middle region they become attached to the straight tubules which here, being without sexual function, lose their identity; in the posterior region of the kidney, where all the early units have degenerated and no straight tubules are formed, the units of the functional kidney become attached to secondary collecting-trunks, derived as outgrowths from the archinephric duct and obviously homologous with the ureters of T r i t o n. In fact, the only difference between E a n a and Triton in this region is that the latter has the ureters, whose walls must therefore be furnished with some muscular support, outside the main mass of the kidney. The whole course of the development of the kidney of the frog may be presented in tabular form: SEXUAL UNITS. (Units of the first generation.) A. EABLYSET. ('Early units', Gray, 1930.) (1) Anterior Region . . . Few develop to a functional condition. (2) Middle and Posterior Region . Develop rapidly to a functional condition, but degenerate at about the same time as the pronephros.
Page 1 and 2: The Development of the Amphibian Ki
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Page 31 and 32: Quart. Journ. Micr. Set. Vol. 78, N
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ment of the Kidney, and the Development of the - Journal of Cell ...

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