624 EXISTENCE OF A HEAD-KIDNEY 



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 crlomerulus and the aorta. We have reason to 



o 



think that the corpuscles and vascular channels in the glome- 

 rulus are developed in situ. The stalk connecting the glome- 

 rulus with the attachment of the mesentery varies in thickness 

 in different sections, but we believe that the glomerulus is 

 continued unbroken 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 fusing 

 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 glomerulus of the Malpighian body comes into view it is 

 seen to be derived from the same formation as the glomerulus 

 of the head-kidney (PI. 28, 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 glome- 

 rulus most fully developed, being prior to that in which the 

 head-kidney appears, it is not possible to determine with cer- 

 tainty the position of the glomerulus in relation to the head- 

 kidney. After the development of the head-kidney it is found, 

 however, as we have already stated, that the glomerulus termi- 

 nates at a point just in front of the anterior opening of the 

 head-kidney. It is less developed than before, but is still pre- 

 sent up to the period of the atrophy of the head-kidney. It 



