144 PROFESSOR MARSHALL AND EDWARD J. BLES. 



Concerning the posterior end of the Miillerian duct, we find that 

 in frogs of this age, the end of the first year, the duct may be traced 

 back as far as the anterior end of the Wolffian body. It lies to the 

 outer side of the aorta, and is exceedingly slender along the greater 

 part of its length ; towards its hinder end the lumen disappears, 

 and the duct becomes a solid rod of cells. "We have traced this 

 into the Wolffian body, but have failed to determine how it ends, or 

 in what manner its further growth backwards is effected. We note, 

 however, that it does not in our specimens lie quite so close to the 

 peritoneum as Hoffmann describes and figures. 



In a second year's female frog the Miillerian duct is formed along 

 its whole length, but still has an exceedingly small lumen, or is 

 actually solid along part of its course. In front, its opening into 

 the body cavity is now in the position which it occupies in the 

 adult. 



Before leaving the head kidney, we may refer briefly to the 

 glomerulus and the changes which it undergoes. The glomerulus 

 of the head kidney arises as a sacculated outgrowth from the ventral 

 and outer wall of the aorta, which bulges outwards into the body 

 cavity opposite the nephrostomes. At the time of hatching of the 

 tadpole, this dorsal part of the body cavity is, as already noticed, 

 practically the only part present, for though the splitting of the 

 mesoblast extends down the sides of the body to the ventral surface, 

 yet the two layers, somatic and splanchnic, are in close contact, owing 

 to the great mass of the food-yolk, except at this upper or dorsal 

 angle. The glomerulus therefore appears at this period to be in a 

 special cavity, which, later on, opens into the general ccslom on absorp- 

 tion of the yolk and further development of the abdominal viscera. 

 At a later stage still, as shown for a 23 mm. tadpole in Fig. 6, T, the 

 part of the tody cavity in which the glomerulus lies becomes partially 

 boxed in by fusion of the outer wall of the lung with the peritoneal 

 covering of the head kidney. The partition so formed is only an 

 incomplete one, inasmuch as the part of the coelom lodging the 

 glomerulus communicates freely with the general body cavity poste- 

 riorly, and also anteriorly in front of the root of the lung. 



The development of the glomerulus keeps pace with that of the 

 head kidney. It is large up to about 23 mm. (Fig. 6, N G), but 

 from that stage commences to dwindle. Its size and relations at 



