784 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
in close proximity to the intermediate cell-mass. LEREBOULLET observed that in Perca 
this structure develops earliest posteriorly, for he failed to trace it anteriorly, though at 
a later stage, about the time of hatching, he was able to follow its whole course (No. 93, 
p. 633) anteriorly and posteriorly, In some species a fold is developed, not a solid rod. 
RosENBERG seems to have been the first to speak of it as a diverticulum from the 
somatopleure (No. 138), and OzLLacHER, HorrMaN, and others have confirmed this view. 
Ryper asserts that “ the development of the renal organs in different genera of Teleosteans 
differs greatly in detail” (No. 141, p. 533), and this would certainly appear to be so, for 
in Salmonoids, which the observers named chiefly investigated, the origin of these ducts 
as longitudinal diverticula pushed dorsally towards the epiblast, as a groove-like fold, in 
fact, of the peritoneal cells, has been clearly shown (see OELLACHER, No, 114, fig. 18,, 
Taf. iv.; Horrman, No. 69a, Taf. iii. fig. 3). Yet in Gadoids and Pleuronectids it is by 
no means clear that this is the precise mode of origin. In the earliest condition yet 
observed in these pelagic forms a longitudinal blastema or solid cylinder is formed on the 
outer margin of the intermediate cell-mass, just as we find in the chick. Defined at 
first in the region of the mid-trunk, this blastema rapidly extends forward to the pectoral 
region, but posteriorly it develops more slowly and is ill defined. A lumen is formed by 
the radiate arrangement of its cells, which separate at their common point of junction, 
and it is now outlined throughout its whole length some days before the embryo emerges. 
In an ovum (haddock) of the ninth day these structures are very distinctly seen as a pair 
of simple ducts, with walls consisting of a single layer of columnar cells, and extending from 
the pectoral region to the root of the tail, Anteriorly each tube is folded upon itself, 
turns inward towards the notochord, and ends in a trumpet-shaped infundibular opening, 
a condition exactly according with that described by Batrour and Parker in Lepidosteus 
(No. 18, p. 415); but in that species the authors agree with RosENBERG and OELLACHER, 
that it is a hollow outgrowth of the somatopleure, and freely communicates with the body- 
cavity. The two ducts are widely separated, but as they pass backward gradually approach, 
and, curving down in the anal region, they meet and unite beneath the notochord in an 
unpaired common portion (wv, Pl. VIL. fig. 8, and in section fig. 6a), which is originally 
of small capacity and provided with thick walls. At first the ducts are somewhat super- 
ficial (prn, Pl. VII. figs. 1, 2, 3), as is implied in their mode of origin, being dorsally 
directed outgrowths of the proximal somatopleure; but they undergo a change of position 
similar to that exemplified in the chick, and lie ventro-laterally to the notochord (sg, PI. 
VIL. fig. 4), and ultimately protrude into the peritoneal cavity (sg, Pl. XI. fig. 14). 
Ryper did not make out the mode of termination in Gadus, and he supposed that the 
urinary vesicle opens either directly into a cloaca or the terminal portion of the intestine. 
The continuity of the walls of the ducts (sy) with the bilobed upper part of the urinary 
vesicle (wv) is clearly demonstrated in section (Pl. VIL. figs. 7, 11), and the urimary 
vesicle itself has an outlet in its early condition of an interesting nature. LEREBOULLET 
described in Perca the first condition of the ducts, and says that each must be a secreting 
