S32 Mil. J. S. BUDGET! ON THE STRUCTURE 



the i)n)iK'pliios of Ainia aud that of Pulypterus is not possible, seeiufi; that the stage I 

 have described is undoubtedly only the last stage in the history of the pronephros. 



ylcipciitier ^ has a very long ]ironephric chamber, with at tirst six, later four, funnels 

 leading from tlic ])ronephric chamber. 



Lcpidosfeus, according to Beard -, has also at first a long chamber with three 

 funnels, later a shorter one with two, aud finally, according to Balfour ^ and Parker, 

 only one funnel leads from the pronephric chamber. 



It is of course conceivable that at au earlier stage Polypterus has more than 

 one funnel leading from the pronephric chamber ; but I think that this is not probable, 

 seeing how widely is the glomus separated from the convoluted portion of the duct. 



Lebedinsky* has described the pronephros of Calamoichthys n.'s, mingled with the 

 anterior tubules of the mesonephros, somewhat as Semon describes the pronephros in 

 IchthyophU^^. Seeing, however, that his " larvas " measured 12 cm. and 15 cm. 

 respectively, I think it would be surprising if in these young Calamoiclithys there 

 should remain traces of a pronephros which in Polypterus is already degenerating at 

 3 cm., aud has completely disappeared at 9 cm. It is still more surprising that the 

 larval head-kidneys of two creatures so closely allied as Polypterus and Calamnkhthys 

 bear no resemblance one to another. But it is not clear to me by what means the 

 author of this account has distinguished between the tubules, " outer and inner 

 funnels," &c. of the pronephros from those of the mesonephros. I am bound 

 to conclude therefore that what Lebedinsky has described as " Vorniere " in 

 CalamoichtLys are some of the anterior tubules of the mesonephros, possibly accessory 

 undeveloped ones, and that the pronephros (" Vorniere ") has already disappeared. 



At this stage the mesonephric tubules are already becoming complicated in the fore 

 part of the body. There are from two to five glomeruli to each body-segment, and 

 about the same number of tubules opening into the segmental duct (text-fig. 4). The 

 accessory glomeruli and tubules arise close to the segmental duct, while the older 

 formed ones become displaced and are found nearer the dorsal aorta towards the 

 middle line (text-fig. 4, m.cps.). In the hinder half of the mesonephros the glomeruli 

 become fewer and fewer, and the arrangement of the tubules simpler, while to each 

 body-segment there is now found one glomerulus and one tubule opening into the 

 segmental duct (text-fig. 4, Jc.t.). Throughout this portion of the body there is found 

 lying immediately to the outer side of the genital ridge (ovary) and ventral to the 

 segmental duct a strip of thickened peritoneal epithelium (PI. XXXV. figs. 1, 2, 3, 4, 

 5, 6, 7, 8, ov.d.) ; this will eventually form the dorsal wall of the oviduct. From the 

 twenty-fourth to the fortieth segment there is found opening upon this thicTiened ridge 

 in each segment a nep>hrostome communicating ivith the glomerulus (PI. XXXV. 

 figs. 0, 4, neph., & text-fig. 4, p. 331). 



' Jungersen, Zool. .inz. 1893, pp. 464, 469. " Ajiat. Anz. Bd. x. p. 94. 



' Loc. cit. "* Jeu. Zcitschr. 1S91. 



° Arch. mikr. Acat. slir. p. 216. 



