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 1st 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 1st 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 (PI. 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, T 7 ^ 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 T 5 ^- 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, f inch in length — from the roof of the 

 body-cavity almost to the level of the summit of the neural arch. 



