70 ADAM SEDGWICK. 



(fig. 1^) are continued as small channels in the intermediate 

 cell mass or Wolffian blastema, and remain, enlarging when 

 the Wolffian tubules are formed later, I have been unable to 

 ascertain. Neither have I been able to satisfy myself as to 

 another interesting point, viz. do those rudimentary nephro- 

 stomata correspond to the Wolffian tubules subsequently 

 developed? In the chick's twentieth segment never more 

 than three nephrostomata can, at the most, be made out, 

 yet there are four or five primary Wolffian tubules later. 



Has this increase been caused by the development of more 

 tubules than there were nephrosomata, i. e. by intercalation, 

 or has it been caused by a change in the relation of the parts 

 to one another, due either to an elongation of the proto- 

 vertebra or to the travelling forward of the tubules as they 

 are developed behind ? 



I shall return to the consideration of this point in a future 

 paper. 



The mode in which the Wolffian blastema behind the 

 twentieth^ segment breaks up into tubules, so far as I have 

 been able to ascertain it, is the following : — A number of 

 vesicle^, either oval or circular, lined by columnar cells, and 

 lying just internal to the Wolffian duct, make their appear- 

 ance (fig. 5). In longitudinal sections it may be seen that 

 these vesicles closely adjoin one another antero-posteriorly. 

 They are developed from those cells of the Wolffian blastema 

 immediately adjoining the, inner border of the Wolffian duct. 

 By a study of transverse sections it appears that each vesicle 

 is continuous ventrally with that part of the Wolffian blas- 

 tema which has not undergone conversion into the walls of 

 the vesicle, and which lies just internal to the vesicle. The 

 cells of this part of the Wolffian blastema very soon arrange 

 themselves round what appears as a continuation of the 

 original vesicle (fig. 11). From the inner and dorsal wall 

 of the last-formed structure a glomerulus is ultimately de- 

 veloped. The whole structure grows enormously, and gives 

 rise to the Malpighian body and complicated coils of the 

 later W^olffian tubule. At about the stage of development 

 represented in fig. 11 the tubules acquire an opening into 

 the Wolffian duct. 



The question as to whether or no there are outgrowths 

 from the Wolffian duct to meet the independently developed 



^ Vide also fig. 125, of Kolliker's 'Entwick. gesch. der Menschen u. 

 der. h. Thiere.' 



' I reserve an account of the development of the tubules in front of the 

 twentieth segment, as my observations on this point are not yet suffi- 

 ciently complete to enable me to speak with certainty. 



