74 ME. SWALE VINCENT ON THE 



ureter, including the whole of the so-called head-kidney, is simply a great mass of 

 lymphatic tissue, and does not contain a single uriniferous tubule or Malpighian body." 

 He next proceeded to examine Esox lucius, Osmerus eperlanus, Anguilla anguilla, and 

 Lophius piscatorius among Teleosts, and found pretty much the same condition as in 

 Ganoids. He does not speak very positively about the Angler, but believes that 

 tubules were present in all parts of the kidney. He sums up " that the pronephros, 

 though found in the larvce or embryos of almost all the Ichthyopsida, except the Elasmo- 

 branchii, is always a purely larval organ, which never constitutes an active part of the 

 excretory system in the adult state." Balfour describes the lymphatic tissue of the 

 so-called head-kidney as formed of trabecular work and cells resembling a lymphatic 

 gland. This tissue is very vascular, with a regular plexus of very large capillaries, 

 which appear to have distinct walls, and which pour their blood into the posterior 

 cardinal vein as it passes through the organ. With regard to the function of this 

 tissue Balfour suggests that this is either the formation of lymph-corpuscles or of 

 blood-corpuscles, and he was inclined provisionally to regard it as a lymphatic gland. 



Parker (Brit. Assoc. Reports, 1882) stated that in many instances the mesonephros 

 has grown forward in front of the air-bladder, and taken the place of the pronephros. 



In studying Bactylopterus volitans, Calderwood (25) found the pronephros entirely 

 separated from the body-kidney, and situated anterior to the abdominal cavity in the 

 same transverse plane as the heart. On section this head-kidney appeared to be a 

 functional kidney, only it did not contain so many tubules as the body-kidney. In 

 Cyclopterus lumpus he finds that not till the fish has become sexually mature does its 

 head-kidney commence to degenerate. Calderwood concludes that in adult Teleosteans 

 the renal function is performed in some instances by the body-kidney only, in others 

 by the head-kidney only, and in others, probably a very limited number, by both 

 the body- and head-kidneys. Besides Bactylopterus he is aware of only one instance 

 where the head-kidney is described as possessing tubules and Malpighian bodies, 

 viz. Fierasfer (Emery 26 and 27) 1 . 



Weldon (35 and 36), in a paper on the head-kidney of Bdellostoma, describes a 

 lobulated glandular body lying in front of the secreting part of the kidney, which he 

 suggests is " a part of the embryonic kidney, modified in connection with the needs of 

 the animal to perform some unknown function in the elaboration or purification of 

 the blood." Then he instances Balfour's description of the lymphatic head-kidney in 

 Teleosts and Ganoids as being a further illustration of a modification of a part of the 

 embryonic kidney into an organ like a lymphatic gland. Next he suggests that in 

 higher Vertebrates the suprarenal capsules are similarly modified portions of the 

 primitive kidney. He continues, " In Teleostei suprarenale are, at all events, frequently 

 absent 2 ; or, as I would suggest, they are represented by the greatly-metamorphosed 



1 In a later paper (Scientif. Trans. Roy. Dublin Society, vol. v. (ser. ii.) ix. 1895, Survey of Fishing- 

 grounds, &c.) Holt and Calderwood add to this list Mora mediterranea and all the species of Macruridae. 



2 The italics are mine. — S. V. 



