TWELVE FIGURESIn most anamnia the mcsonephros begins its activity while the pronephros is still a t its functional height. For a time both organs function together; then the pronephros undergoes degeneration and the rnesonephros becomes the only functional excretory organ. This entire complex of processes has without further consideration been transferred t o the relation between the mesonephros and the metanephros, and the question whether the mesonephros is actually functional in the amniota has never been seriously considered. Weher ('97) was the first to take it up and he endeavored to answer it in the following manner. He coinpared thc time of degeneration of the mesonephros with that of the development of the metanephros; when he found that the rnesonephros degenerated before the metanephros could exercise an excretory function, he has assumed that the mesonephros did not function, for if it had been active and had then degenerated before the metanephros had begun its activity, there must have been a certain period of development during which there was no excretion. Let us adopt this same method in considering the special case of the function of the human mesonephros. Already in an embryo of 19.4 mm. greatest length the majority of the mesonephric tubules are so far in process of degeneration that they cannot be regarded as having an excretory function. Of the 35 tubules of this embryo only four are actually still intact. In an embryo of 22 mm. greatest length none of the mesonephric tubules were capable of functioning; in all the tubulus secretorius had separated from the tubulus collectivus. If one inquires how far the development of the metanephros has progressed a t this time, one finds that embryos of 22 mm. have just reached the anlagc of the second generation of uriniferous tubules. The first generation, however, has as yet no fully formed Malpighian corpuscles. If, then, the mesonephros had functioned as an excretory organ, there must necessarily have been an interruption of this function on its degeneration. Consequently, I regard the question as to the functioning of the mesonephros as settled; it does not function as an excretory organ. This does not, of coui*sc, imply that it may not have been active in another manner unknown to us.

No abstract

No abstract

No abstract

No abstract