On the Early Development of the Anterior Part of the 

 Wolffian Duct and Body in the Chick, together with 

 some Eemarks on the Excretory System of the Yerte- 

 BRATA. By Adam Sedgwick, M.A., Eellow of Trinity 

 College, Cambridge. With Plate III. 



The following paper is divided into two parts. The first part 

 contains an account of observations on the development of the 

 Wolffian duct and anterior Wolffian tubules in the chick, being 

 supplementary to my paper on the "Kidney of the Chick ."^ 

 The second part is devoted to a discussion of the vertebrate 

 excretory system in general. 



I. Early Development of the Wolffian Duct and Anterior 

 Wolffian Tubules in the Chick. 



The first trace of the Wolffian duct is visible in an embryo 

 ■with eight protovertebrae as a slight projection from the inter- 

 mediate cell mass towards the epiblast in the region of the 7th 

 and 8th protovertebrae. The projection also extends back 

 behind the region of the protovertebrae for a short distance. 

 In a chick with nine or ten protovertebrae a similar condition 

 is found, i.e. a projection from the intermediate cell mass 

 towards the epiblast in the region of the 7th, 8th, 9th, and 10th 

 protovertebrae, and for a short distance behind the region of 

 the protovertebrae. 



In a chick with ten protovertebrae the projection is beginning 

 to show signs of separation from the intermediate cell mass at 

 certain points. The appearance presented by the rudiment of 

 the Wolffian duct in the 10th segment of a chick with ten seg- 

 ments is shown in fig. 1. 



In a chick with eleven protovertebrae the rudiment of the 

 Wolffian duct is still present as a projection from the inter- 

 mediate cell mass in the region of the 7th, 8th, 9th, 10th, and 

 11th protovertebrae ; but behind the region of the protovertebrae 

 it has grown back for a short distance between the epiblast and 

 mesoblast as an irregular cord of cells not connected to the 

 peritoneal epithelium. A partial separation of the Wolffian 

 duct from the intermediate cell mass is now effected in the 

 region of the 7th to the 10th protovertebrae. This separation 



' "Development of tlie Kidney in its relation to the WolflQan Body in 

 the Chick," 'Quart. Journ. Mic. Sci.,' vol. xx. 



