262 MALPHIGIAN BODIES. 



alluded to in the description on p. 256. The development of 

 the 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 XX. 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 bod}^ It assumes (PI. XX. 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 

 w^all becomes thinner, and formed of flattened cells, except in the 

 interval 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^ has given of the 

 formation of these bodies in the embryonic Mammalian 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 segmental 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 xx., a longitudinal vertical section 

 through a portion of the kidney between stages 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 — 

 there is a complete segmental tube {s.t) which opens at its upper 

 1 Journal of Anatomy and FiiT/siology, Vol. ix. 



