784 PROFESSOR W. 0. 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. 

 Eosenberg seems to have been the first to speak of it as a diverticulum from the 

 somatopleure (No. 138), and Oellacher, Hoffman, and others have confirmed this view. 

 Ryder 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 2 , 

 Taf. iv. ; Hoffman, 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 Balfour 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 (uv, PI. VII. 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. 

 VII. fig. 4), and ultimately protrude into the peritoneal cavity (sg, PI. XL fig. 14). 

 Ryder 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 (sg) with the bilobed upper part of the urinary 

 vesicle (uv) is clearly demonstrated in section (PI. VII. figs. 7, 11), and the urinary 

 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 



