6 BALFOUR AND SEDGWICK. 



kidney. It is represented in figs, e and f, PI. II gl, and is 

 seen to form a somewhat irregular projection into the body 

 cavity, covered by a continuation of the peritoneal epithelium, and 

 attached by a narrow stalk to the insertion of the embryonic 

 mesentery {me) . 



In the interior of this body is seen a stroma with numerous 

 vascular channels and blood-corpuscles, and a vascular connec- 

 tion is apparently becoming established, if it is not so already, 

 between the glomerulus and the aorta. We have reason to think 

 that the corpuscles and vascular channels in the glomerulus are 

 developed in situ. The stalk connecting the glomerulus with 

 the attachment of the mesentery varies in thickness in different 

 sections, but we believe that the glomerulus is continued un- 

 broken throughout the very considerable region through which 

 it extends. This point is, however, difficult to make sure of 

 owing to the facility with which the glomerulus breaks away. 



At the stage we are describing, no true Malpighian bodies are 

 present in the part of the Wolffian body on the same level 

 with the anterior end of the glomerulus, but the Wolffian body 

 merely consists of the Wolffian duct. At the level of the pos- 

 terior part of the glomerulus this is no longer the case, but here 

 a regular series of primary Malpighian bodies is present (using 

 the term ^' primary '' to denote the Malpighian bodies developed 

 directly out of part of the primary segmental tubes), and the 

 glomerulus of the head-kidney may frequently be seen in the same 

 section as a Malpighian body. In most sections the two bodies 

 appear quite disconnected, but in those sections in which the 

 (jlomendus of the Malpighian body comes into view it is seen to 

 be derived from the same formation as the glomerulus of the 

 head-kidney (Plate II, fig. f). It would seem, in fact, that the 

 vascular tissue of the glomerulus of the head-kidney grows into the 

 concavity of the Malpighian bodies. Owing to the stage we are 

 now describing, in which we have found the glomerulus most fully 

 developed, being prior to that in which the head-kidney appears, 

 it is not possible to determine with certainty the position of the 

 glomerulus in relation to the head-kidney. After the develop- 

 ment of the head-kidney it is found, however, as we have already 

 stated, that the glomerulus terminates at a point just in front of 

 the anterior opening of the head-kidney. It is less developed 

 than before, but is still present up to the period of the atrophy 

 of the head-kidney. It does not apparently alter in constitu- 

 tion, and we have not thought it worth while giving any further 

 representations of it during the later stages of its existence. 



Nummary of the develoj)ment of the head-kidney and glomerulus. 

 — The first rudiment of the head-kidney arises as three successive 

 grooves in the thickened germinal epithelium, connected by ridges 



