DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 787 



it is interesting to see a large glandular structure, such as the so-called head-kidney, 

 which may be made out in early embryos, and which is from the first closely associated 

 with the main haemal vessels of the trunk. The lymphatic system, with its plasma and 

 leucocytes, is really intermediate between a venous and an arterial system, and is 

 associated with the various serous membranes, pleural, peritoneal, pericardial, and others. 

 It is not surprising that large lymphatic masses should occur so near the centre of the 

 blood-system, and though Balfour was not inclined to regard them as parts of the 

 true kidney at all, they cannot at any rate be regarded solely as degenerate pronephric 

 structures. Weldon, in his brief but interesting paper on Bdellostoma (No. 156), 

 suggests that such masses are represented in all vertebrates by the suprarenal bodies. 

 In Bdellostoma the archinephric or segmental duct is separated from this anterior mass, 

 though in some specimens, possibly younger, traces of the continuity of the two could be 

 made out. In embryonic Teleosteans the continuity is very patent, and in the adult 

 condition renal tubules still ramify amongst the lymphatic tissue, as Balfour found in 

 Esox, Lophius, and Osmerus. In the last species a single tubule alone passes into the 

 vascular lymphatic mass. It would appear, indeed, as if the embryonic pronephros in the 

 process of degeneration were usurped by the antenephric lymphatic structures, the 

 proximity of both favouring this, while the persistence of stray tubules in the posterior 

 part indicates the pronephric portion. Grosglik's researches upon various adult 

 Teleosteans (Cyprinus carpio, Esox lucius, Rhodeus amarus, Gastrosteus aculeatus) con- 

 firm Balfour's view, as he found coexisting in the region of the head-kidney lymphatic 

 tissue and remains of the atrophied pronephros surrounded to some extent by the cardinal 

 vein, while some pronephric tubules still pierced the lymphatic meshwork (No. 60, 

 pp. 605-611). Emery, however, maintains that the pronephros persists permanently in 

 such as Fierasfer and Zoarces ; while in other forms, as Blennius, it is provided with 

 glomeruli and tubules, and in Merlucius esculentus it presents the peculiar structure of 

 the Wolffian body. In all it persists as a recognisable pronephros (No. 53a), a view which 

 Hyrtl held ; while Rathke and Stannius concluded that in Cyprinus the head-kidney 

 is degenerate, and bereft of tubules, a view now generally adopted. The segmental duct 

 precedes the development of the Wolffian body, and cannot therefore be a mesonephric 

 duct, as Balfour suggests (No. 11, p. 701); it is in fact a pronephric duct, or more 

 truly it is archinephric, for the pronephros is secondarily developed as a convoluted 

 anterior portion. It is possible that this duct may not represent the primitive condition, 

 but rather a segmental canal bereft of its serial segmental tubules and nephrostomes, 

 save the single infundibulum at its anterior termination.* The view generally accepted 

 however, is that which interprets it as a primitive non-metameric renal duct. The ducts 

 retain their simple tubular character in the adult condition, and pass along the latero- 

 ventral margins of the fully-developed renal masses. In the last larval stages, within a 



* The fact, however, that some segmental tubes, consisting of nephrostome, capsule, and convolutions, develop in 

 Elasmobranchs independently of the duct, and later connect by their originally blind end, may indicate that the serial 

 condition is secondary. It illustrates at any rate their separation and independent coexistence, whatever the explana- 

 tion may be. 



