DEVELOPMENT OF SPELERPES BILINEATUS ■ 223 



it has been found that the transverse neural folds of the Urodeles 

 lie nearer the upper pole than those of the Anura. With the 

 exception of Barfurth, who, believing that his own methods had 

 'grosser Mangel/ locates the head of the Axolotl near the equa- 

 tor, the workers on Urodeles, (viz., Eycleshymer '95 , '04, Jordan 

 '93, Brachet '03), agree in locating the head of the embryo near 

 the upper pole. Schultze ('90) would locate the entire embryo 

 of the Axolotl on the upper hemisphere, but an examination of 

 his figures shows that they can be equally well interpreted in 

 accordance with the view just mentioned. In this same paper, 

 Schultze maintains that the entire embryo of the frog develops 

 on the upper hemisphere and gives excellent data for his position. 

 But Pfluger ('83), Born ('93) and Hertwig ('93) in compressed 

 eggs, observed that the frog's embryo developed on the lower 

 hemisphere, its head lying near the equator. No one, as far as 

 I know, has compressed the eggs of a Urodele and recorded the 

 embryo as appearing on the lower hemisphere. Among the work- 

 ers who have endeavored to locate the embryo by means of punc- 

 tures, Eycleshymer ('93 and '04) is the only one who has found 

 the head of Rana as also of Bufo and Acris, appearing at the upper 

 pole. Apparently, there is real variation in the position of the 

 head of the embryo in different species, as has been shown by 

 Morgan ('06), when he found in centrifuged eggs that the head 

 of the toad appeared somewhat higher up than did that of the 

 frog. Morgan and Tsuda ('94), and Wilson ('03) agree in locat- 

 ing the transverse neural folds of the frog slightly above the 

 equator, while King ('01) and Morgan ('06), as already mentioned, 

 find that the embryo of the toad appears nearer the upper pole 

 of the egg. It is interesting to note that, in the eggs of Hypo- 

 geophis, as described by Brauer, the embryo must form entirely 

 above the equator, owing to the large mass of yolk present. 

 Ikeda ('02) presents results which are somewhat variable but in 

 general tend to support this view. 



With the data at hand, we are justified in concluding that the 

 amphibian embryo develops almost entirely in a vertical half 

 of the egg, the tail appearing near the lower pole, while the ante- 

 rior end of the body develops in greater or less degree in the upper 



