DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 785 
organ solely, assuming the excretory function later, when the ovoid dilation (urinary 
vesicle) establishes a communication with the lumen of the enteron (No. 93, p. 633). 
Kuprrer draws attention to a strand of cylindrical cells connecting this receptacle and 
the hind gut, “ uniting,” he says, “ with the epithelium of the gut” (No. 87, p. 224); but 
he appears not to have made out, any more than LeREBoOULLET, an actual communica- 
tion between the two. Yet such is the case. A distinct tubular connection exists; but 
the walls of the vesicle (wv) as well as the enteron (ig) are extremely plastic and mobile, 
vermiform movements being frequent, so that the lumen between the two becomes wider or 
narrower, and at times appears to close up, though the communication is usually readily 
seen (Pl. XX. fig. 13). Throughout their whole length, these excretory canals, including 
the urinary vesicle, exhibit simply a wall of nucleated cubical cells—a single layer of 
cylindrical epithelium. Such is the condition of the renal tract until the time of hatch- 
ing, viz., a pair of cylindrical tubes, which pass along each side of the subnotochordal 
heemal trunks, to terminate, after curving inward and downward in an infundibular 
opening. In front of the crozier-shaped loop (prn, Pl. XI. fig. 11, and Pl. XXI. 
fig. 6) a mass of trabecular tissue lies, into which tubules appear to enter to some 
extent, but this loose connective is also penetrated from the front by the growing basilar 
plate. The simple character of the embryonic renal organs in the Teleostei may be taken 
as evidence of a primitive condition, in which no metamerism is seen, the simple duct, 
which is truly an archinephric duct, forming a loop in front, and communicating with the 
pleuroperitoneal cavity, while posteriorly it passes into the hind part—a cloacal section, 
in fact—of the enteric tract. 
During the greater part of embryonic life this simple condition continues, and the 

infundibular openings do not seem to increase in number; whereas in Amphibians several 
(three or four) are developed, and in Selachians they form a series. When the young 
fish emerges, the anterior end of the kidney shows signs of growing complexity, the folds 
of the loop increasing, and a vascular glomerulus being developed in front of the swim- 
bladder near each nephrostome. A little later the nephrostome of each side and its 
adjacent glomerulus are gradually enclosed in a capsule, this fibrous sac shutting off both 
structures from the general body-cavity. A section just behind the occipital region 
(Pl. XXVI. fig. 4) shows one of a pair of such capsules in the middle line and below the 
median hemal trunks (ao and cv). On the lower and inner side of each capsule a 
vascular meshwork (g/) is present, while the nephrostome of the head-kidney opens on the 
outer side of the capsule. The rudiments of the single pair of glomeruli are seen in the 
newly emerged embryo, and are not fully developed until some days later; but in 
Gastrosteus and like forms, which issue from the ovum in a more advanced condition, the 
later features are already exhibited. RypeEr states that in Clupea alosa there is no 
evidence of the existence of a nephrostome or of the presence of median glomeruli until 
long after hatching (No. 141, p. 534), and this is certainly remarkable, though in the 
Gadoids and others great variations are observable, the renal organs being fairly advanced 
in P. platessa a day or two before hatching, whereas in P. flesus and P. limanda they. 
VOL. XXXV. PART III, (NO, 19). 6H 
