klDNEY IN' RELATION TO WOLrilAN BODY IN THE CUICK. 73 



adjoining the primary tubules^ and from an inspection of his 

 figures it is evident that these cell masses are situated close to 

 the Malpighian body of the primary tubule. In the chick I 

 have sought in vain for some clear sign in the development 

 of these cells which would enable a comparison to be insti- 

 tuted with Elasmobranch development. 



In the chick the cells of the Wolffian blastema do not all 

 seem to be used in the formation of the primary tubule. 

 Those, that are not, seem to collect at a special point, i. e. 

 just dorsal to that part of the primary tubule which will 

 become eventually the Malpighian body. The cells of the 

 primary tubule are especially thick at this point, and per- 

 haps they give rise to some of the cells for the secondary 

 tubule (fig. 11). Even if this is the case — and we may look 

 upon the secondary tubule as an outgrowth from the primary 

 tubule — it is impossible to say where the secondary tubule 

 so formed opens into the WolflSan duct. 



This brings me to another difference between the dorsal 

 tubules of the chick and those of Elasmobranchs. In the latter 

 they all open into the collecting part of a primary Wolffian 

 tubule. In the former they all open independently into the 

 Wolffian duct, or it may be into an outgrowth from it, but 

 separately from the primary tubule. This latter point I am, 

 as above stated, obliged to leave open at present. The 

 number of primary tubules present in one segm.ent seems to 

 be fairly constant, five or six to each segment, throughout 

 the Wolffian body, except quite in front, where there seem 

 to be fewer. All segments, from the twentieth to the 

 thirtieth inclusive, contain five or six primary tubules. In 

 front of the twentieth segment they seem gradually to de- 

 crease. In the first segment in which a fully developed 

 tubule appears there seems only to be one, the number 

 increasing rapidly to the twentieth. 



The dori-al tubules appear in greater number behind 

 than in front. In tlie twenty-eighth segment I have 

 counted as many as four, but more are possibly developed 

 later. They correspond in number to the primary tubules, 

 i. e, if there are five primary tubules in the twenty-eighth 

 segment, there are twenty secondary tubules (five sets of 

 four). The most anterior segment in which a secondary 

 tubule appears is the twenty-first or twenty-second; I have 

 not been able, however, to localise it exactly. 



Develojment of kidney. — The development of the Wolffian 

 blastema from the intermediate cell mass has been described 

 as far back as the thirty-fourth segment j i. e. to the openino- 

 of the Wolffian duct into the cloaca; it is never seen 



6 



