492 DEVELOPMENT OF ELASMOBRANCH FISHES. 



Malpighian body is intimately linked with that of the secondary 

 connection between two segments. They are both products of 

 the metamorphosis of the vesicle which forms the termination of 

 the segmental tube proper. 



At about stage O this vesicle grows out in two directions 

 (PL 21, fig. 10), viz. towards the segment in front (p.x) and 

 posteriorly into the segment of which it properly forms a part 

 (mg). That portion which grows backward remains continuous 

 with the third division of its proper segment, and becomes con- 

 verted into a Malpighian body. It assumes (PL 21, figs. 6 and 

 10) a hemispherical form, while near one edge of it is the opening 

 from a segmental tube, and near the other the opening leading 

 into a tubulus of the kidney. The two-walled hemisphere soon 

 grows into a nearly closed sphere, with a central cavity into 

 which projects a vascular tuft. For this tuft the thickened inner 

 wall of cells forms a lining, and at the same time the outer wall 

 becomes thinner, and formed of flattened cells, except in the in- 

 terval between the openings of the segmental tube and kidney 

 tubulus, where its cells remain columnar. 



The above account of the formation of the Malpighian 

 bodies agrees very well with the description which Pye 1 has 

 given of the formation of these bodies in the embryonic Mam- 

 malian kidney. My statements also agree with those of Semper, 

 in attributing the formation of the Malpighian body to a 

 metamorphosis of part of the vesicle at the end of the seg- 

 mental tube. Semper does not however enter into full details 

 on this subject. 



The elucidation of the history of the second outgrowth from 

 the original vesicle towards the preceding segment is fraught 

 with considerable difficulties, which might no doubt be over- 

 come by a patient investigation of ample material, but which I 

 have not succeeded in fully accomplishing. 



The points which I believe myself to have determined are 

 illustrated by fig. 10, PL 21, a longitudinal vertical section 

 through a portion of the kidney between stages O and P. In 

 this figure parts of three segments of the kidney are repre- 

 sented. In the hindermost of the three the one to the right 



1 Journal of Anatomy and Physiology, Vol. IX. 



