hall: mesonephros and mullerian duct in amphibia. 97 



It will be remembered that I have claimed, ou gi'ounds of analogy, 

 that the Miillerian evagination in Rana sylvatica represents three 

 evaginatious, and that evidence of at least two was not lacking. That 

 evidence was twofold : (1) The cell-mass which proliferates to form the 

 Mullerian duct sometimes evaginates at two (and possibly three) points. 

 (2) In a case where the third nephrostome had not fused with the 

 other two, there was present an evagination near the fused, anterior two, 

 and a disk (representing an evagination) near the posterior, free one. 

 It has been shown that in Hyla versicolor the anterior nephrostome is 

 independent of the fused posterior ones, and that there is an evagination 

 associated with the former as well as one with the latter. With two 

 evaginations patent, I hoped to find evidences of a third by a careful 

 study of the posterior one, wliich, theoretically, should consist of a com- 

 bination of two. I have looked in vain for such evidence as was found 

 in Rana. The posterior evagination, although often mucli elongated 

 antero-posteriorly, never showed distinct signs of a separation into two 

 pits. Fortunately, however, I found one case in which all three nephro- 

 storaes had remained distinct ; that is, the two posterior had not under- 

 gone the normal fusion. As a parallel variation in Rana gave rise to a 

 separation of the Mullerian evagination into two, it seemed probable that 

 in this case three fundaments might be distinguished. In effect, the 

 condition was as follows. Dorsal to the first nephrostome was a very 

 conspicuous evagination. The second and third nephrostomes w^ere far 

 back of the first and quite near each other, the second being ventral and 

 somewhat anterior to the third. Figure 85 (Plate 7) represents a sec- 

 tion passing through the posterior edge of the second nephrostome and 

 just anterior to the third (some cilia of the latter are cut). There will 

 be noticed a rather marked thickening {evg. -2) dorsal to the second 

 nephrostome. While not very conspicuous, it is so restricted, — so 

 clearly marked off from the surrounding epithelium, — and resembles 

 so closely in staining properties, etc., the disk which always precedes the 

 formation of a Miillerian eviagination, that there is no doubt in my own 

 mind that it really represents a second evagination. The evagination j 

 associated with the third nephrostome is typical. It is shown in 

 Figure ^Q (evg. 3), which is from the second section behind the 

 nephrostome. 



Ic will be seen that in the development of the Mullerian duct, Hyla 

 versicolor occupies a place midway between Ambly stoma and Rana 

 sylvatica. In the presence of well-defined evaginations in connection 

 with more than one nephrostome, the oviducal development approaches 



