926 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



cranium and the pharyngeal roof below. Further back these glandular organs enlarge, 

 and, as two preparations seem to show, they become lobulated, while the vessel on the 

 inner side is surrounded by large nucleated cells. Pigment-corpuscles, moreover, appear 

 at the side of the apertures and near the aorta. Toward the posterior border of the 

 cranium, where a short conical spur abuts on the notochord on each side, the renal organ 

 proper, or pronephros, commences in the form of numerous coils of the segmental duct 

 (PI. XXIII. fig. 2, prn) ; moreover, shortly behind, in the middle line below the aorta, 

 two symmetrical spaces occur, into each of which a round vascular mass (glomerulus) 

 having a glandular appearance, projects, the outer side of each aperture being free 

 (PI. XXVI. fig. 4, gl.). The pigment-corpuscles greatly increase, the main mass being 

 situated dorsally over the segmental ducts, but also between and below them. Besides 

 the ducts a quantity of glandular tissue (apparently Balfour and Parker's lymphatic 

 tissue) occurs at the inner and inferior border of the region . The coils of the segmental 

 duct form a considerable mass as they pass backward, but they soon diminish. The 

 course of each, laterally, varies in those species of Teleosteans in which a swim-bladder 

 is developed, the large capacity of this median structure causing the ducts to be widely 

 separated anteriorly. In the post-larval cod, \ inch long, they pass along the side of the 

 swim-bladder by a gently descending course to the urinary bladder. The increase in the 

 cellular matter (which stains deeply) surrounding the tubules of the pronephros is very 

 marked in the post-larval stages, and in the young gurnard, £ inch long, it forms quite a 

 large lobate mass enclosed in a very delicate membrane or capsule, the two glomeruli being 

 imbedded in this apparently glandular matrix. A similar development of these small 

 cells, which stain deeply, is seen in the cod when T 5 ¥ of an inch in length, and much 

 dense pigment is developed around the pronephros. The ducts, when traced back- 

 ward at this stage, pass in the wolf-fish over the urinary bladder, and posteriorly 

 curve round, and debouch into the bladder by a very sharp downward deflection. By 

 and by only a single duct remains with a connective-tissue investment, in which pigment- 

 corpuscles occur all round, except at the inner and inferior border. Subsequently a small 

 solid mass of nucleated cells is seen at the inner and inferior border of the duct ; but no 

 definite structure can be made out, and it soon comes to an end, to be succeeded by 

 similar bands often passing toward the opposite duct. Moreover, in some sections a 

 tubular structure indicates that these are probably segmental tubes in an early condi- 

 tion. These sections are, however, situated high up — close by the sides of the aorta, 

 but they do not appear to connect with it, and they have lax cellular walls. Soon the 

 cardinal vein becomes single, and frequently the cells referred to form a thin band over 

 it. Posteriorly the segmental ducts seem to diminish rather than increase in size, and 

 the large cardinal vein widely separates them. By the diminution of the cardinal (caudal) 

 vein the ducts again approach, and the space between the notochord and the rectum 

 increases by the downward curve of the latter, while the fold of peritoneal mesentery, 

 suspending the gut, disappears. The segmental ducts also move further from the 

 notochord, and their lower ends merge into a dilated common part — the urinary vesicle — 



