DEVELOPMENT OF ELASMOBRANCH FISHES. 268 



extremity into an irregular vesicle, prolonged behind into a 

 body which is obviously a developing Malpighian body, m.g^ 

 and in f7'ont into a wide tube cut obliquely in the section 

 and ending apparently blindly (j). x). In the preceding seg- 

 ment there is also a segmental tube (s. t) whose opening into 

 the body cavity passes out of the plane of the section, but 

 wliich is ao^ain connected with a vesicle dilatinoj behind into 

 a Malpighian body (m. g) and in front into the irregular tube 

 {l')-^) as in the succeeding segment, hut this tube is now con- 

 nected (and this could be still more completely seen in the 

 segment in front of this) with a vesicle luhich 02:>ens into the 

 thick-walled collecting tube (fourth division) of the pi^eceding 

 segment close to the opening of the latter into the Wolffian duct. 

 The fact that the anterior prolongation of the vesicle ends 

 blindly in the hindermost segment is due of course to its ter- 

 minal part passing out of the plane of the section. Thus lue 

 have established between stages and P a connection between 

 each segmental tube and the collecting tube of the segment in 

 front of that to ivhich it properly belongs; and it further appears 

 that in consequence of this each segment of the kidney contains 

 two distinct coils of tubidi ivhich only unite close to their common 

 opening into the Wolffian duct! 



This remarkable connection is not without morpholo- 

 gical interest, but I am unfortunately only able to give 

 in a fragmentary manner its further history. During the 

 gi'eater part of embryonic life a large amount of interstitial 

 tissue is present in the embryonic kidneys, and renders them 

 too opaque to be advantageously studied as a whole ; and 

 I have also, so far, failed to prepare longitudinal sections 

 suitable for the study of this connection. It thus results 

 that the next stage I have satisfactorily investigated is that 

 of a nearly ripe embryo already spoken of in connec- 

 tion with the adult, and represented on PI. xix. fig. 5. This 

 figure shews that each segmental tube, while distinctly 

 connected with the Malpighian body of its own segment, 

 also sends out a branch towards the secondary Malpighian 

 body of the preceding segment. This branch in most cases 

 appeared to be rudimentary, and in the adult is certainly 

 not represented by more than a fibrous band, but I fancy 



