OF THE MULLERIAN DUCT OF AMPHIBIANS. 519 



so because, in the first place, the figures themselves indicate a change in position of the 

 segmental duct ; and secondly, because I have failed to find in Triton, or in any of the 

 other forms examined by me, appearances such as Hoffmann shows, except ivhere there 

 has teen a change of position of the segmental duct. Jungersen, too, has examined 

 Triton carefully without seeing what Hoffmann describes, — open communication between 

 the segmental and Miillerian ducts. 



Semon, MacBride, and Jungersen all agree in ascribing the entire first Anlage of 

 the Miillerian duct to the ccelomic epithelium. 



Semon says of Ichthyophis : " Im Bereich der Vorniere konnte auf diesem Stadium " 

 (the first in which he found the Anlage) " uberhaupt nicht der Vornierengang in Frage 

 kommen da dieser bei seiner enormen Schlangelung unmoglich den schnurgeraclen 

 Muller'schen Gang von sich abspalten oder aus einem Teil seiner Wandung erzeugen 

 konnte. . . . Auch in den unteren Abschnitten im Bereich der Urniere, wo der Vor- 

 nierengang durchaus gestreckten Verlauf besitzt, habe ich an keiner Stelle unci auf 

 keinem Stadium je irgend welche Beziehungen des Vornierenganges zur Peritonealfalte 

 aus der sich der Muller'sche Gang bildet, entdecken konnen." 



MacBride in Eana finds a groove in the peritoneum immediately ventral to the one 

 persisting nephrostome of a frog of 28 mm. long.* The "very columnar" epithelium 

 of the groove is continued out over the surface of the pronephros and beyond it ; and the 

 groove itself when traced backwards is found to end in a solid thickening of the epithelium. 



* MacBride regards this nephrostome as being the first, and not, as Hoffmann had said, the third, of the 

 nephrostomes of the undegenerated pronephros. And Jungersen takes the same view, though he recognises that 

 the closing is from before backwards in Triton. Both MacBride and Jungersen ground their belief solely on the 

 fact that the persisting nephrostome is anterior to the glomerulus, whereas in young forms the glomerulus is situated 

 between the second and third nephrostomes. From the facts already mentioned as to Salamandra atra it appears 

 that the position of the glomerulus is by no means constant ; but this becomes still more apparent from a study of 

 an anurous form. In Alytes obstetricans the younger stages show the glomerulus between the two posterior nephro- 

 stomes ; but older forms are more or less altered. One specimen of 25 mm. was found by me to have the glomerulus 

 extending from three sections anterior to the second nephrostome, back as far as the opening of the third nephrostome, 

 while another specimen, 39 mm. in length, has all three nephrostomes anterior to the glomerulus ; and I have observed 

 various intermediate stages. Moreover, in all the types that I have studied, the degeneration of the pronephros itself 

 has been from before backwards ; and a remarkable partial closure of the anterior pronephros is observable prior to its 

 complete closure ; thus there are various quite obvious stages in the degeneration of the nephrostomes, and these 

 appear in succession, first in the anterior nephrostome, and only later in the second, or second and third. I may 

 illustrate the actual process by describing what I have seen in Alytes : — One specimen 36 mm. in length has all three 

 nephrostomes open, but the anterior one does not open directly into the body-cavity ; the actual mouth of the funnel 

 has been closed over anteriorly and laterally, so that a transverse section through it shows an apparently blind ciliated 

 tube running close up to the epithelium. A passage, however, is left open posteriori}', and in this case there is a 

 new mouth in the fourth section behind the true nephrostome. The chief noticeable effect is to make the opening 

 more ventral as well as more posterior. The posterior nephrostomes open directly into the ccelom. In another 

 specimen, 39 mm. in length, the backward tunnelled passage from the funnel of the first nephrostome is still longer, 

 and forms a perfectly distinct antero-posterior tube immediately under the epithelium. One of 47 mm. in length 

 shows quite similar appearances, while another of 50 mm., in which the anterior of the pronephros has been replaced 

 by blood-spaces, has only two left ; and as these occur in the still undegenerate part of the pronephros, it is easy to 

 identify them as the second and third ; on one side the second nephrostome opens into the body-cavity by a new 

 posteriorly directed aperture. Similar observations on Triton, Salamandra atra, S. maculosa, and Axolotl confirm the 

 view thus arrived at, that a change of position of the mouth precedes a closing of the nephrostomes. As the prone- 

 phros shrinks at the same time, a condition that resembles what was described by Van Wype for the Selachians is at 

 least led up to though I cannot say I have yet seen actual fusion of the nephrostomes. 



