hall: MESONErHROS AND MULLERIAN DUCT IN AMPHIBLL 105 



in patches. MacBride saw no sign of a splitting of the pronephric duct 

 as described by Hoffmann. He thinks it highly improbable that the 

 portion just back of the pronephros takes any cells from the pronephric 

 duct on account of tlie degenerate condition of the latter. Posteriorly, 

 the growing cord comes nowhere in contact with the Wolffian duct. 



Gemmill ('97) describes the development of the MliUeriau duct in 

 Eana temporaria and Pelobates fuscus. The evagination or groove 

 appears lateral [ventral] to the third nephrostome, and development 

 proceeds much as in Triton punctatus (as described by him), with this 

 important difference, — the growing duct comes nowhere in contact with 

 the Wolffian duct. Wliile its tip is too close to the oviducal welt to 

 affirm that it takes no cells from that structure in Rana temporaria, in 

 Pelobates cases were seen-on both sides where the tip was undoubtedly 

 free. The author's description of the cephalic displacement of the ostium 

 agrees with my own for Rana sylvatica. 



Amniota : Mammalia. 

 It is not my intention to discuss the many contradictory accounts 

 which have been given of the origin and development of the Mulleriau 

 duct in Amniota. For a resume of this subject the reader is referred to 

 Burger ('94, '94"). According to the researches of Kip ('94, '94*), mam- 

 mals seem to present the nearest approach in the development of the 

 Mullerian duct to that found in Amblystoma, although from the account 

 of its development in the chick given by Balfour and Sedgwick ('79), 

 birds also show a close similarity. The parallel between Kip's ('94, '94") 

 description and mine is so close that I shall recapitulate briefly his 

 observations on Insectirora (Tupaia, Talpa, Erinaceus) and Rodentia 

 (rabbit, mouse). 



Tupaia : On the ventral surface of the anterior end of the mesone- 

 phros there is a thickening of the epithelium about 200 micra in length, 

 which forms a plate of uniform thickness. At three succe!5sive points of 

 this plate, cell proliferation takes place to form three massive cones, which 

 then become pits opening into the coelom.^ The inner ends of these 

 (or rather of the first two, as the third generally degenerates) fuse, and 

 the resulting cord grows back and applies itself to the blind anterior end 

 of the Wolffian duct. The evaginations grow wider and fuse at their 



1 The number of evaginations is variable. In one case but one was found ; in 

 another, four. 



