786 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



are more rudimentary. The waste-products taken along the renal ducts originally pass 

 directly from the body-cavity, but they are by and by conveyed from the special excre- 

 tory Malpighian capsules into the urinary vesicle behind, a condition which remains 

 essentially unaltered in the adult. The archinephric duct does not really close early in em- 

 bryonic life, as has been stated (No. 48, p. 13), but opens into a special closed part of 

 the body-cavity. With the further development of the anal region, the unpaired enlarged 

 portion into which the ducts pass posteriorly communicates not with the rectum some 

 distance from the external orifice as in the figure before referred to, viz., PL XX. fig. 13, 

 but by a special passage with separate opening posterior to the anus, as in a cod the 

 third week after emerging — a condition also shown in the gurnard three weeks old 

 (PL VII. fig. 9). Of the series of segmental tubules and glomeruli seen in Elasmobranchs 

 there is no trace in Teleosteans ; but though the renal organs are so simple in these 

 latter forms, the interpretation of the various parts is not devoid of uncertainty. 



Teleosteans, it is generally held, agree with Cyclostomes, Amphibians, and Ganoids in 

 possessing a pronephros ; but, in all, it is a larval structure, and is supposed to disappear 

 in the adult. We have seen that in the embryos of the Gadoids, flat fishes, and 

 gurnards an anterior trabecular meshwork (x) lies in front of the archinephric duct, and 

 that this duct itself exhibits a much convoluted fore end (prn, PL XL fig. 11), with a 

 nephrostome communicating with a glomerulus. The mid-portion of the duct becomes 

 more or less convoluted, while the posterior portion remains comparatively straight, 

 though on its dorsal side a large development of cellular tissue and small sinuous tubules 

 takes place at a late or post-larval stage (PL XXIII. fig. 2). 



In the adult we usually find an enlarged anterior paired structure, the head-kidney or 

 pronephros succeeded by a pair of elongated bodies, indisputably renal, which are much 

 swollen terminally, often united, and traversed on their ventro-lateral margins by a pair 

 of excretory ducts. Balfour examined various species of Teleosteans in the adult 

 condition, and came to the conclusion, in opposition to Kosenberg, that the so-called 

 head-kidney is not truly renal, though he did not deny the persistence of the larval 

 pronephros in the adult stage (No. 13, p. 15). In Osmerus eperlanus, Esox lucius, and 

 Anguilla, the fore part of the renal mass consisted in the main of vascular lymphatic 

 tissue, while the true kidney-substance extended posteriorly. In Lophius piscatorius, 

 which, according to Hyrtl, possesses a head-kidney only, lymphatic tissue, traversed by 

 tubules alone, was found. This lymphatic tissue may represent the convoluted enlarge- 

 ment of the archinephric duct, or merely a compact agglomeration of the loose cellular 

 tissue lying external to the ductus Cuvieri and cardinal veins. It would appear that 

 the latter is, in a large degree, true, the fore part being more emphatically trabecular, 

 while the hind part consists of degenerate kidney-substance, so that Balfour's view most 

 probably represents the facts, viz., that the so-called head-kidney is really a large 

 lymphatic gland, concerned in the production of blood or lymph-corpuscles, while the 

 hind portion is a remnant of the embryonic head-kidney. Except for certain lymph- 

 spaces in the caudal region, the lymphatic system is but feebly represented in fishes, and 



