22 ADAM SEDGWICK. 



cavity. This is at once clear on inspection of figs. 16, 17, 18. 

 These figures are taken from the 13th segment of a chick with 

 thirty-four protovertebrse. There was a section not figured 

 between fig. 17 and 18, otherwise the sections are successive, 

 fig. 16 being the anterior. 



In fig. 16 is seen the commencement of the peritoneal funnel 

 as a bay lying between the Wolffian duct and mesentery. 



In fig. 17, a glomerulus [gl.) has appeared projecting into this 

 bay. In the next section, not figured, the bay was almost 

 closed up by an approximation of its edges, while in fig. 18 the 

 bay is completely shut off from the body cavity, and we have a 

 section of a true Malpighian body with its contained glomerulus. 



Fig. 18 clearly corresponds to fig. 15 of the previous* stage, 

 while fig. 17 corresponds to fig. 14, the difference being that a 

 distinct cellular projection (^/.) has appeared at the point where 

 the projection of cells from the Wolffian duct joins the inter- 

 mediate cell mass. 



I have given a diagram (fig. 22) representing an ideal longi- 

 tudinal dorso-ventral section through two of these Wolffian 

 tubules at this stage. This diagram has been made from a study 

 of many embryos showing the development of the external 

 glomerulus. 



The open peritoneal funnel is represented at />./!, the arrow 

 pointing into it. Through it is projecting the anterior part of 

 the glomerulus (^^.), that part which I shall call the external 

 glomerulus. A transverse section through this part would 

 give the appearance represented in fig. 17. 



Into the closed hinder part of the tubule (m(5.) is projecting 

 the hinder part of the glomerulus {i. gl.\ which I shall call the 

 internal glomerulus. It was not possible to represent satis- 

 factorily in this diagram the AVolfiian duct, which, obviously 

 from its position in transverse section, would not be seen in a 

 longitudinal section passing through the attachment of the 

 glomerulus. 



In fig. 23 is represented somewhat diagrammatically a trans- 

 verse section through a chick with thirty-three protovertebrse, 

 i. e. from a slightly younger embyro than that from which 

 figs. 16 — 18 were taken, in which the cord of cells connecting 

 the Wolffian duct with the cavity of the glomerulus had acquired 

 a distinct lumen, the cavity of the Wolffian duct being here 

 distinctly continuous with that of the bay in which is placed 

 the rudimentary external glomerulus, and so with the body 

 cavity. At subsequent stages this part of the tubule appears to 

 persist but only in a rudimentary fashion. 



The next stage which I propose to describe was found in a 



