16 ADAM SEDGWICK. 



12th — 15tli segments inclusive; (3) that found behind the 15th 

 segment. 



In a previous paper^ I have described at some length the 

 early development of the Wolffian body behind the 16th segment^ 

 and I have there shown that that part may be divided into two 

 parts, each characterised by a peculiarity in the early develop- 

 ment. In this paper I shall make but little reference to the 

 development of the Wolffian body in this region, confining 

 myself almost entirely to that part lying within the area of the 

 7th to the 15th segments inclusive. 



Development of Wolffian Tubules in region of 1th — Wth 



Segments. 



The Wolffian tubules and Wolffian duct in this region attain 

 but a slight development. They may almost be said to have 

 reached their highest point at the stage with fourteen proto- 

 vertebrse, the only difference in later stages being the develop- 

 ment of a lumen in them. The lumen in the tubule may 

 acquire an opening into the Wolffian duct in some cases. In 

 this case the strinp: of cells seen in fig. 6 becomes very short, 

 and the Wolffian duct appears as a narrow groove in the peri- 

 toneal epithelium. This state of things is usually found in 

 chicks with from nineteen to thirty-two protovertebrse. 



The Wolffian duct in this region exhibits great variations in 

 calibre, and in later stages parts of it appear to atrophy, and 

 isolated portions are found connected with rudimentary tubules. 

 An enlarged section of the Wolffian duct in front is nearly 

 always found as Gasser^ has described. The duct and tubules 

 in this region appear entirely to atrophy in chicks with more than 

 thirty-five protovertebrse. 



I have not thought it worth while to preserve figures of the 

 duct and tubules in this region of the Wolffian body after their 

 first appearance, as the arrangement just described may be easily 

 observed in sections of an embryo chick of the third day. 



The interest in the development of this region lies in the fact 

 of the continuiiy of development of the Wolffian tubules and 

 Wolffian duct. It has always appeared to me astonishing that 

 the Wolffian duct developed as a continuous ridge from the inter- 

 mediate cell mass, which, from our knowledge of Elasraobranch 

 development, may be called the peritoneal epithelium, should 

 entirely separate from it and thfen secondarily become connected 

 with it by tlie tubules of the Wolffian body. My investigations, 

 which have been made with some care on a large number of 



' Loc. cit. ' Loc. cit. 



