No. 446.] DESMOGNATHUS FUSCA. 



\27, 



had made their appearance on the surface of the yolk, reminding 

 one forcibly of similar embryos e. g., those of certain Teleosts, 

 that resuh from meroblastic eggs. Too sharp a distinction 

 between the holoblastic and meroblastic type cannot, however, 

 be drawn, since there are numerous transition forms, as that of 

 Salamandra maculosa, in which the egg is 4-5 mm. in diameter, 

 and the first two cleavage planes, although they slowly cut their 

 way around the egg on the outside, often fail to divide the yolk 

 internally, " so dass die Furchung in den ersten Stadien partiell 

 ist " (Ziegler loc. cit., p. 249, on the authority of Gronroos, 

 1903). A similar condition has been produced experimentally 

 in the frog's egg by O. Hertwig (1897). The eggs of the 

 Gymnophiona, which are the largest of all Amphibian eggs, 

 (7-8 mm. in Hypogeophis rostratus) are at first typically mero- 

 blastic, with a germinal disk that spreads gradually over the 

 yolk; but during and after gastrulation the yolk becomes 

 divided up into large cells, so that the eggs are ultimately 

 holoblastic. 



In these latter, also, as well as in the eggs of Salamandra and 

 Desmognathus, there is a noticeable array of blood vessels upon 

 the yolk, which at first sight closely resembles a true yolk circu- 

 lation, but which in reality consists of the vessels which normally 

 appear superficially in the region distended by the yolk mass, 

 and thus, although they may receive nutriment from the yolk, 

 they are in no .sense true vitelline vessels. The vems ot thi.s 

 region, though not the arteries, could be closely followed in the 

 two series from which Figs. 4 and 5 were taken, and are shown 

 to be three in number, one median and two lateral. The meclian 

 vein lies along the mid-ventral line of the s^ 

 scarcely noticeable posteriorly, but increasing 

 picks up several lateral branches. It passes along 

 (concave) aspect of the liver and enters the sinus venosus in 

 company with the hepatic vein. By its VO^^'^^ --^^^^'^t 

 undoubtedly corresponds to the abdominal vein «f ^he adu 

 and thus, although it may be also a potential portal it cannot be 

 very definitely related to the true vitelline veins of merobla^ti 

 embryos. l/the same way the -^^^%^ZX^ 

 identical with the large cutaneous veins whicn iie ^ 



eriorly 



