The development of the urinogenital organs of the lamprey. ß3 



as exhibited by Teleostei, Amphibia etc. These generations appear 

 successively and are derived by common consent from the tubules of 

 the primary generation. The secondary, tertiary etc. tubules are, 

 therefore, indirectly traceable to the intermediate cell- mass, or meso- 

 nephrotome of the embryo. They are an all-important factor in in- 

 creasing the volume and in destroying the primitive metameric character 

 of the mesonephros of the Vertebrates in which they occur. The 

 condition of the mesonephros in Fetromyzon probably arose from 

 a condition like that of the Amphibian by a contraction of the gener- 

 ations of tubules till they all appeared simultaneously. Instead of 

 a long stretch of the mesonephros being mapped out by primary and 

 then filled in by successive generations of secondary, tertiary etc. 

 tubules, only short pieces of the whole mesonephros are formed from 

 time to time with the definitive number of tubules. Since the tubules 

 of the mesonephros and metanephros have very probably arisen, both 

 phylogenetically and ontogenetically in response to a need for more 

 excreting surface, it may be a matter of indifference from a physio- 

 logical point of view which of these two modes is adopted. 



c) The Glomus, Glomerulus and Vascular System. 



The problems suggested by the vascular system of the Vertebrate 

 renal organs are no less difficult than those suggested by the excretory 

 tubules themselves. This fact sufficiently explains the confusion in 

 which the student finds the whole subject of the glomerular apparatus 

 of the pro- and mesonephros. The confusion has been largely brought 

 about by the undue generalization of certain conditions first observed 

 in the Amphibia. As Felix has recently shown (1897 b, p. 311 et seq.) 

 GoETTE and Semon are largely responsible for conducting us into this 

 maze of wrong conceptions concerning the morphological relations of 

 the glomerulus. A "pronephric chamber" of the Amphibian pattern 

 was saught and found by these authors where is never existed, and 

 curiously enough both singled out Fetromyson as especially Amphibian 

 in the structure of its pronephros. 



Goette (1891, p. 57 and 60) finds the somatic and splanchnic 

 layers of the Petromyzon embryo fusing under the anterior and 

 posterior ends of the pronephros, and proceeds forthwith to homologize 

 these structures with the folds which cut off the pronephric chamber 

 in Amphibia from the general coelom, notwithstanding the fact, that, 

 as he himself shows, neither of these folds have any demonstrable 

 connection with the pronephros and are, moreover, converted into 



