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. VIL 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 () lies in front of the archinephric duct, and 
that this duct itself exhibits a much convoluted fore end (prn, Pl. XI. 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. BaLrour examined various species of Teleosteans in the adult 
condition, and came to the conclusion, in opposition to RosenBerc, 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 Hyrvt, 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 
