The development of the urinogenital organs of the lamprey. 55 



also lead us to accept Rückert's hypothesis. Price worked on a 

 few embryos of the Myxiuoid Bdellostoma (PoUstotrema) stouti of the 

 Californian coast and published his results in three brief papers 

 (1896 a, 1896 b and 1896 c). These results and their interpretations 

 were necessarily fragmentary and unsatisfactory, and the interpretations 

 of these interpretations by Semon (1896, 1897 a and 1897 b), Felix 

 (1897 a) and Rabl (1896) have only added to the confusion. This 

 confusion has been still further increased by Semon's and Spengel's 

 (1897 a, 1897 b) controversy on the renal system of Myxine. The 

 timely appearance of Maas' paper (1897) on young specimens (8,5— 

 13 cm long) of Myxine glutinosa makes any extended consideration 

 of these various papers superfluous. As Maas refers to Price's work 

 only in foot-notes, he evidently had not seen the work till his own 

 was well nigh finished. This accounts for certain discrepancies which 

 Maas promises to explain in a future publication (p. 499). I am in- 

 clined to lay more stress on Maas' results than on those of Price, 

 since the former is dealing with stages which can be more easily 

 interpreted as they are nearer the known adult condition of the 

 excretory system of Myxinoids than the few embryonic stages studied 

 by Price. To bring the results of Price's work into complete accord 

 with those of Maas, one supposition must be made, viz. that Price 

 mistook the formation of the pronephric duct from discontinuous 

 metameric diverticula of the coelom for the formation of the meso- 

 nephros, surely a pardonable blunder if he has actually, as I believe, 

 committed it. The following are my reasons for believing that Price 

 did not see the formation of the mesonephric tubules: First, I doubt 

 Price's statement (1897 b, p. 220) that "the series of embryos is 

 sufficiently complete, so that it can be said positively, that the tubules, 

 which in the adult have been described as mesonephric tubules, come 

 from tubules which have just been shown to arise as pronephric 

 tubules", since I find nothing to convince me that his figs. 12, 13 

 and 14, tab. 17, really represent mesonephric tubules, or that the 

 bodies marked gl are really glomeruli. Second, Maas has shown that 

 mesonephric tubules are forming in the posterior half of the body of 

 Ilyxine (presumably 8,5 cm long) independently of the pronephric 

 duct (figs. 4 — 8, tab. 38), which is already established in this region. 

 The mesonephric tubules figured by Maas are similar to the meso- 

 nephric tubules of Fetromyzon and may perhaps be formed in the 

 very same way, except that they are metameric. Then, too, the ad- 

 vanced mesonephric tubules which have acquired an opening into the 



