11)6 THE FROG. 



but there is no doubt tliat the greater part of the length, and 

 perhaps the whole, of the duct arises independently of the 

 Wolffian duct ; and apparentl^y from a modified strip of perito- 

 neal epithelium which runs parallel to the Wolffian duct, along 

 its outer side. 



Towards the close of the metamorphosis, and during the 

 absorption of the tail, a patch of modified peritoneal epithelium 

 appears on the ventral surface of the now rapidly disappearing 

 head kidney, below a nd to the outer side of the nephrostome s. 

 of which, as a rule, o nly one persists at this sta ge (Fig. 88, Ks). 

 This patch of epithelium differs from the general peritoneal epi- 

 thelium in its cells being columnar instead of squamous in shape. 

 A longitudinal groove forms on the surface of this patch of 

 columnar epithelium, to the outer side of the nephrostome ; and, 

 by fu sion of its lip s, the groove becomes a tub e, o pening in fron t 

 into ^the bodyj 3avity, a nd ending blindly beh ind. This tub e 

 is the first formed part of the Mtillerian duc t ; it lies very close 

 to the anterior end of the segmental duct, but it is not clear 

 that there is any connection between the two ; i t is quite in- 

 rlftpanrlpnt, nf +.1ia nAphmstnmp which c loses up and disap pears 

 ver y shortly after this sta ge . 



The Miillerian duct extends forwards, as an open groove, some 

 distance in front of the point at which the duct is first formed ; 

 and, by closure of the lips of the groove from behind forwards, 

 the mouth of the duct is carried forwards, outwards, and down- 

 wards, round the anterior end of the body cavity, to its adult 

 position at the root of the lung. 



The growth backwards of the Mtillerian duct is effected bv 

 a longitudinal band of cells, which appears a little to the outei* 

 side of the Wolffian duct, but quite independent of this, and 

 apparently derived directly from the peritoneal epithelium. This 

 band, which is continuous with the hinder end of the Mtillerian 

 duct, ultimately becomes tubular, and acquires posteriorly an 

 independent opening into the cloaca. 



In the male frog the Mtillerian duct sto]3s at tH ^Rtagp 

 In t he female it undergoes further chan p -es by which it becom es 

 con verted into t he oviduct. It increases in length, becoming 

 sinuous, and ultimately convoluted along the greater part of its 

 length ; its walls thicken greatly, and the epithelium lining them 

 gives rise to the gelatinous secretion which is poured out over the 



