880 Mr Sedgwick, ' Glomerulus of the head-kidney! [May 3, 



I may here state that it is not a continuous structure, but con- 

 sists of a series of external glomeruli, each of which corresponds 

 and is continuous with the glomeruli of the Malpighian bodies 

 found in this part of the trunk. 



I will commence the description of the development at the 

 time when the segmental tubes have reached the stage of develop- 

 ment figured byKolliker^ and myself ^ At this stage each of them 

 in the anterior region of the Wolffian body has the form of an 

 S-shaped string, with a narrow opening into the body cavity, the 

 lower limb of the S being formed by the intermediate cell mass, 

 and the upper limb by a column of cells which connects the inter- 

 mediate cell mass with the Wolffian duct. 



In the region where each external glomerulus is afterwards 

 found the openings into the body cavity which are homologous 

 with the peritoneal openings of the segmental tubes in Elasmo- 

 branchs widen out very considerably, and a lumen is continued 

 from them into the intermediate cell mass on the one hand, and on 

 the other hand into the column of cells which forms the upper 

 limb of the S and connects the intermediate cell mass with the 

 Wolffian duct^ 



That part of the segmental tube which will afterwards become a 

 Malpighian body is therefore in the region where an external 

 glomerulus will subsequently be formed connected with the body 

 cavity b}^ a short tube. This tube rapidly widens out, especially 

 anteriorly, to such an extent that it soon appears as a shallow bay 

 in the body cavity. Thus each opening at this stage forms a bay, 

 wide and shallow anteriorly, becoming deeper and narrower as we 

 pass backwards, until finally behind it is separated from the body 

 cavity altogether, and there is seen in section a Malpighian 

 capsule precisely resembling a developing Malpighian capsule in 

 the hinder region of the Wolffian body*. In this bay and in the 

 small part behind continuous with the bay, but separated from the 

 body cavity, which are together serially homologous with a Mal- 

 pighian capsule and the funnel leading from it into the body 

 cavity, a small glomerulus soon appears attached to the dorsal wall. 



1 EntivicMimgsgeschichte des Menschen u. der hbheren Thiere, p. 201, 2nd ed. 



^ Quart. Journ. Mic. Sc, April, 1880, pi. xvii., fig. 1. 



=* This may best be understood by examining fig. 11, pi. xvii. in my paper 

 akeady referred to {Q. J. 31. S., April, 1880). If the primary WolfBan tubule (wt^) 

 here represented were connected with the peritoneal epithelium at the point where 

 the line from ivt'^ cuts it, and it were open to the body cavity at that point, an 

 appearance similar to that which I have attempted to describe would be obtained. 

 Or perhaps a better idea of the structure may be obtained from fig. 6, pi. xx. in 

 Balfour's Monograph on the Development of Elasmohranch Fishes. If st were 

 very short and wide, so that mg were widely open to the body cavity, the figure 

 would resemble a developing Wolffian tubule in this anterior part of the chick's 

 Wolffian body. 



4 loc. c/f.'fig. 11. 



