(5-20 DR GREGG WILSON ON 



sections before a part is reached in which a lumen occurs. The lumen is distinct till 

 within a few sections of the end of the foundation. The solid rod that forms the tip of 

 the foundation lies external to the segmental duct, touching it, but independent of it, 

 and remote from the ccelomic epithelium. In the section immediately posterior to that 

 which contains the last cells of the rod-like apex there is no appearance of budding of 

 the cells of the mcsonephric duct, such as one would expect if growth backwards of the 

 Mullerian duct were dependent on it ; and there is no indication of any contribution of 

 cells from the coelomic epithelium to add to the growing tip. 



It thus appears clear that in this specimen growth backwards is by apical prolifera- 

 tion ; and I conclude that, as in the formation of the anterior end, so in the manner of 

 growth backwards there is essential agreement between Chelone and Crocodilus. 



LIST OF WORKS QUOTE,!) IN THIS PAPER. 



(1) Braun, "Das Urogenitalsystem der einheimischen Reptilien," Arh. a. d. Zool. zoot. Inztitut., Wtirz- 

 burg., Bd. iv. Hft. ii., 1877. 



(2) Mihalkovics, " Untersuchungen uber die Entwickelung des Ham- und Geschlechtsapparates der 

 Amnioten," Intern. Monatzsch. fiir Anat. und Hist., Bd. ii. 



(3) Hoffmann, " Zur Entwicklungsgeschichte der IJrogenitalorgane bei den Reptilien," Zeit.f. iviss. Zool., 

 Bd. xlviii., 1889. 



(4) Wiedersheim, " Ueb. die Entwickelung des Urogenitalapparates bei Crocodilen und Schildkrbten," 

 Arch. f. mikr. Anat., Bd. xxxvi. 



(5) Burger, " De Ontwikkeling van de Miiller'scbe Gang bij de Eend en de Bergeend," Tijdxch. d. Med. 

 Dierlc. Vereen. (2), iv. 



(6) Gregg Wilson, " The Development of the Mull. Ducts of Amphibia," Trans. Roy. Soc. Ed., 1896. 



DESCRIPTION OF FIGURES. 



Fig. 1. Transverse section through the pronephric region of crocodile of 10 mm. in length, l.r. is the 

 lateral ridge that in older stages forms the secondary connection between the alimentary canal and the body- 

 wall. 



Fig. 2. Section across crocodile 12 mm. in length, showing thickened epithelium (m.d.) on the ventral 

 wall of the coelomic diverticulum, anterior to the glomus. 



Fig. 3. Section through the same embryo further back, and showing an extensive lateral epithelial 

 thickening on a level with the anterior end of the glomus. 



Figs. 4 and 5. Sections through the same embryo further back, showing the two posterior extensions 

 of the pronephric thickened plate. 



Fig. 6. Section through tlie same embryo, showing the grooved Mullerian duct foundation in relation to 

 the mesonephros. 



Figs. 7, 8, 9, 10. Sections from a series through an embryo further advanced than stage B, and showing 

 the lateral and ventral extension of the Miillerian duct foundation. 



