146 PROFESSOR MARSHALL AND EDWARD J. BLES. 



hinder end of the kidney. They note also, as has been pointed out 

 by Spengel, Fiirbringer, and others, that the tubules are at first 

 segmen tally arranged, but soon become more numerous than the 

 segments ; and that the most anterior tubules, which extend for- 

 wards to within two or three segments of the head kidney, differ 

 slightly from the posterior ones, and early undergo degenerative 

 changes. 



Sedgwick* has disputed some of the above statements, and states 

 very clearly that in the frog the cells from which the Wolffian tubules 

 arise are "at their first appearance independent of the peritoneum, 

 and only secondarily become connected with it." He suggests also 

 that Fiirbringer has fallen into error through assuming that the 

 details of formation of the extreme anterior end of the Wolffian body, 

 where the tubules are rudimentary and never attain full develop- 

 ment, apply also to the functionally active tubules of the hinder 

 part, or kidney proper. 



Our own observations support Sedgwick's statements. We find 

 that in tadpoles of from 10 mm. to 12 mm. length the Wolffian tubules 

 arise as little masses of cells in the mesoblast between the aorta 

 and the archinephric duct, a little distance from the peritoneum, 

 and quite independent of it. These masses of cells are at first 

 segmentally arranged ; they are ill-defined groups of spherical or 

 slightly branched cells, which rapidly acquire more definite rod-like 

 shape, then become tubular, and growing outAvards meet and open 

 into the archinephric duct, while at their opposite ends Malpighian 

 bodies are formed at a slightly later date. The nephrostomes appear 

 to us to arise as outgrowths from the tubules towards the peri- 

 toneum, and the mode of their formation will be described in the 

 next section. 



Though we feel fully satisfied as to the origin of the Wolffian 

 tubules in the mesoblast independently of the peritoneal epithelium 

 in tadpoles of Puma temporaria, the only species investigated by us, 

 we do not wish to attach much value to the fact from a morphological 

 standpoint. We are rather of opinion that this will prove to be 

 one of the numerous details of development in which the frog does 



* Sedgwick, "On the Early Development of the Anterior Part of the Wolffian 

 Body and Duct in the Chick, together with some remarks on the Excretory System 

 of the Vertebrata," " Quarterly Journal of Microscopical Science," new series, vol. 

 xxi., 1881, pp. 448-450. 



