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 
(Pl. 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 
(Pl. 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 BaLrour 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, 4 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, 4 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 ,°; 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— 
