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). 

 Kupffer 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 Lereboullet, an actual communica- 

 tion between the two. Yet such is the case. A distinct tubular connection exists ; but 

 the walls of the vesicle (uv) as well as the enteron (hg) 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 (PI. 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 

 hsernal trunks, to terminate, after curving inward and downward in an infundibular 

 opening. In front of the crozier-shaped loop (pm, PI. XL 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 hgemal trunks {ao and cv). On the lower and inner side of each capsule a 

 vascular meshwork (gl) 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. Ryder 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. fiesus and P. limanda they 



VOL. XXXV. PART III. (NO. 19). 6 H 



