hall: mesoxepheos axd mullerian duct in amphibia. 89 



disappeared) by a narrow slit (Fig. 46, near marg. p- tab.), that is, the 

 posterior margin of the shelf (Fig. 45, tab.) is still free. Degenerate pro- 

 nephric tubules (Fig. 45, tbl. pr'njjh.) are recognizable. The grooving or 

 folding of the thickened band (which is supported by a fuld of the peri- 

 toneum) now extends for a long distance cephalad from the ostium (Fig. 

 47, evg. 2), instead of for only a few sections, as in Larva XI. It reaches 

 an entire somite anterior to the position of the adult ostium, which is 

 opposite the posterior end of the fourth vertebra. I believe this seem- 

 ingly superfluous anterior portion is utilized in forming the doicnward 

 curve of the anterior end of the adult duct, which, instead of opening 

 near the dorsal line of the body cavity, curves downward and outward 

 around the base of the lung to its final position in the ventral portion 

 of the body cavity. This downward curving seems to be brought about 

 by the progressive restriction of the body cavity anteriorly. 



Figure 47 shows the ostium {evg. 2) two sections anterior to the point 

 where it becomes closed off' from the body cavity. For thirteen sections 

 behind that point, the duet shows two lumina. This may be regarded 

 as evidence of its double origin. 



Thei'e is a rather constant difference in the formation of the Mullerian 

 duct on the two sides of the body. On the left side, the thickened band 

 lies more laterally, and the grooved condition always extends farther 

 forward than on the right side. I have been unable to detect any differ- 

 ence in the formation of the duct in the two sexes. If, however, a larger 

 number of specimens were examined with this special point in view, 

 minor differences might perhaps be found. 



The formation of the "shelf," which is also described by Hoffmann 

 ('86) and Gemmill ('97) as existing in Triton, seems to me interesting. 

 It has generally been held that the glomerular cavity in the Urodela is 

 of little significance, it being a sort of accidental consequence of the 

 temporary fusion of the lung with the body-wall. We see that there 

 exists in Amblystoma a glomerular cavity of an independent and more 



In Figure J the first evagination (the black dot beneath the first nephrostome) has appeared. 

 The epithelial band may be divided into four regions: (1) a portion (tae. e'ih.a) run- 

 ning back from the first evagination ; (2) one (tae. eUh. /3) from the second nephrostome, 

 joining (1); (3) their combined prolongation (tne. e'th.y) above the shelf; and (4) the 

 same (tae. e'tk. y') extending forward beneath the shelf. 



In Figure K'the second evagination has appeared and the first has sent the pre-coelomic duct 

 (dt. pr'coel.) forward and a duct (dt. 1) backward. 



Figures/^, M, A^ scarceh- need further explanation. The second evagination sends back 

 a duct (dt. 2) which fuses with portions of the duct from the first, the remainder of this 

 latter duct, as well as the epithelial band from the first evagination, degenerating. The 

 extent of the fusion of the lung with the body-wall (Fig. /, sep. im. par.) is gradually 

 diminished in the successive stages. 



