354 J. W. KTRKALDY. 



of one without. I will describe first the anatomy of an organ 

 from a Myxine in the latter condition. 



Examined by means of transverse sections, the head kidney 

 is found to be in very intimate relation with the post-cardinal 

 vein (fig. 2). The greater part of it is actually lodged in the 

 vein, whilst the more superficial tubules are embedded in the 

 vascular wall, or lie free in the pericardial cavity. At the 

 posterior end a glomerulus is present (fig. 2, gl.), extending 

 along the inner side of the head kidney for about one fourth 

 of its length. Posteriorly it is enclosed in a sheath of its own, 

 but towards the front end this becomes indistinct, and the 

 glomerulus tissue is interwoven with that of the pronephros. 

 The organ seems, however, to be in a state of reduction, and 

 the vascular supply cannot be clearly made out from any 

 sections. The tubules, which are caught in section in every 

 direction, open into the pericardium on the one hand by means 

 of funnels (fig. 2, /.), and on the other are connected 

 ultimately with a large duct (fig. 2, c. d.), the central duct (9), 

 which, just as has been shown for Bdellostoma, sometimes 

 divides into two or three great anastomosing branches, and then 

 again becomes single. 



In Myxine, however, as Miiller states, the central duct 

 gives off, on the side away from the tubules, outgrowths 

 containing glomeruli (fig. 4, c). In sections towards the 

 hinder end of the organ I find that the glomerulus may, for a 

 short distance, quite fill up the central duct, so that no lumen 

 is visible, and then this reappears a few sections further on 

 (fig. 2, gl. d.). Blood-vessels pass across the vein to break up 

 inside the capsule into the characteristic capillary loop. The 

 efferent vessels return to the capillary network between the 

 central duct and the wall of the vein (fig. 2, c. n.). 



The central duct does not reach to the anterior extremity of 

 the organ ; it stops short, and only a bunch of tubules projects 

 forward. The walls of the duct consist of tall columnar cells 

 of granular protoplasm, each containing a large oval nucleus of 

 coarser granulation (figs. 3 and 6). The cells have rather a 

 ragged appearance at their fore-edge; this is emphasised by an 



