HALL : MESOXEPHROS AND MULLEEIAN DUCT IN AMPHIBIA. 69 



range of the secoudary), one tertiary for each secondary, etc. The 

 develoj)meut of additional dorsal units is continued to a surprisingly late 

 period. Thus I found young, non-functioning units in a large, adult 

 female of E-ana virescens. 



Outer Tulmles ami Nephrostomes. 



As is well known, the outer tubules in Anura, after reaching the peri- 

 toneum, become cut off from the rest of the unit and open into venous 

 spaces (see Fig. 100). This fact I confirmed in Rana sylvatica, Rana 

 virescens, and Hyla versicolor in sections of the larvae, where the cilia 

 at the inner end of the tubule can be very plainly seen extending into 

 venous spaces. lu R. virescens I also confirmed it in the adult by means 

 of the method — -first used by Nussbaum ('80), I believe — • of injecting 

 powdered carmine into the body cavity of the living animal, then fixing 

 and sectioning. 



It seems still undecided whether, in Anura, the outer tubule aflfords 

 at any stage an actual communication between the coelom and the neck 

 of the Malpighian body. At the time when it is still joined to this neck 

 and to the peritoneum it possesses a lumen throughout a part of its 

 length, but more I cannot affirm. Whether the lumen is continuous 

 with the coelom and with the cavity of the Malpighian neck, I found 

 it impossible to determine, as cross-sections of the animal cut it at an 

 unfiivorable angle. After all, the continuity or discontinuity of the 

 lumen is a matter of small theoretical importance, as it is perfectly 

 clear tliat the outer tubule arises exactly as in the Urodela, and that the 

 adult peculiarity is ontogenetically acquired. A matter of more impor- 

 tance is the origin of the large number of nephrostomes which appear 

 as the animal matures. Are they (1) the openings of outer tubules 

 which grow down independently and become cut off fi'om the dorsal sets 

 of units ; are they (2) evaginations of the peritoneum ; or are they (3) 

 developed from the original outer tubules by division] The second and 

 third suppositions seem both to be true. The outer tubules (in an 

 old larva of R. virescens) have every appearance of dividing, and occa- 

 sionally there are also to be seen short, deeply staining, peritoneal evag- 

 inations at a considerable distance from anv older ones. It is of course 

 possible that these arise from cells derived from dorsal units, but I have 

 looked in vain for cell-strands gi'owing out from those units toward the 

 peritoneum. 



