DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 927 
the wall of which superiorly appears to be composed of cylindrical epithelium with a fibrous 
outer investment passing into the connective tissue surrounding it (Pl. XXV. fig. 5). 
The glomerulus on Ist March presents a more distinctly looped arrangement (PI. 
XXVI. fig. 4), the basal regions being narrow and closely applied to each other, the 
free portion having a pear-shaped outline, and in transverse section showing long spaces, 
so that it has a somewhat looped appearance. These chambers above are formed by 
thin membranous walls studded over with small globular cells. The anterior cardinal 
veins, as they debouch into the venous sinus, are outside the glomerulus and the 
pronephros. On 16th March the cellular stroma towards the posterior part of the 
segmental ducts increases superiorly on the sides of the cardinal veins, and above the 
ducts. It soon forms two symmetrical masses above the latter, the constituent cells of 
which are arranged somewhat in rows, so that there is a tendency to a tubular structure. 
A series of vascular spaces, however, develop at the commencement of the urinary vesicle, 
and the tissue disappears. The preparations of 20th April distinctly show in this region 
segmental tubes on a miniature scale. 
These secondary growths, moreover, have extended much further forward. It is 
remarkable that, though the cellular tissue has greatly increased anteriorly, and for 
some distance backwards, no distinct tubes appear there at this date. 
On Ist May the chief change is the increase of pigment round the pronephros, which 
has a proportionally large bulk—the two sides forming on section an area equal to that 
of the alimentary canal. In the glomerulus nothing new is observed. A large vein 
runs down the right pronephros towards its termination, and then bends to the middle 
line. The segmental duct is now reduced to a single canal on each side, and, having 
reached the middle line beneath the aorta, the masses of cells superiorly, that is overlying 
the ducts, become more complex, and segmental tubes branch out—occurring both above 
and below the aorta, and beneath the cardinal vein in the middle line. The segmental 
ducts increase in size as the tubes become numerous, and each, like the ducts, has a 
hyaline investment (PI. XXVI. fig. 3). A granular substance occupies the centre of the 
segmental duct in section (Pl. XXV. figs. 4, 5, 6, and 7). 
The mass of cells, above described in Anarrhichas, is late in appearing in most of the 
other forms studied. In Labrus, j4; inch long, it forms a thick cylindrical column, 
over the two segmental ducts in the terminal part of their course. 
The intimate relation of the pronephros and the posterior cranial nerves is remarkable, 
the large cellular outgrowths of the brain, which mark the egress of the ninth and tenth 
nerves, are closely associated with the cellular stroma of the head-kidney, and the similarity, 
in the early condition, of the nervous and renal tissue is striking, especially at such a 
post-larval stage as that of the gurnard, when ,°; of an inch long. The roots of the 
glosso-pharyngeal and vagus exhibit enormously enlarged ganglionic swellings in the 
example just instanced. The head-kidney, moreover, becomes so greatly increased in 
bulk dorso-ventrally as to extend in the cod, 2 inch in length—from the roof of the 
body-cavity almost to the level of the summit of the neural arch. 
