Development of the Mesonephros in Amblystoma after Early Extirpation of the Duct

Abstract

The mesonephros in Amblystoma develops from the 9th (or 10th) embryonic somite to the twentieth, at the level of the cloaca. The anterior region, corresponding approximately to segments 10-15, bears the usual relation to the gonad and is the so-called “sexual kidney.” The posterior region, more massive and anatomically more complex (due to the presence of secondary, tertiary units, etc.) is the “secretory kidney.” Both regions develop from a continuous band of nephrogenic tissue, the “mesonephric blastema” dorso-medial to and contiguous with the primitive kidney duct or pronephric duct. Very early in differentiation the mesonephric units of both regions establish connections with this duct, which thus becomes the mesonephric duct. There is, however, a marked delay in the development of the posterior region, during which the units of the sexual kidney are well developed and functional; and it is to this region of delayed development that secondary, tertiary, etc., tubules are confined. These statements rest largely on the early work of Hall. 1 Such differences in morphology, chronology and functional relations raise interesting problems of homology.

In view of the early association between the rudimentary mesonephric units of both regions and the duct, it was decided to investigate the result of elimination of the latter upon the origin and differentiation of the former. In Amblystoma the primitive duct (pronephric duct) arises at the level of somites 3 and 4, and gradually grows posteriorly along the ventral border of the row of somites until it reaches the cloaca at the level of somite 20. At stages 26-27, Harrison's Series, the growing end of the duct reaches only to the 8th or the beginning of the 9th somite, and at or prior to this time may be removed without disturbing the mesonephric region.