24 J. GRAHAM KERR. 



the lower pole of the egg than in Lepidosiren, about 30° 

 below the equator instead of abont 10°. It is consequently 

 visible from the beginning when the egg is viewed from the 

 lower pole, forming part of the circumference of the small 

 circle bounded by the edge of the small-celled area. The 

 condition is exactly as in a typical Urodele ^ or Anuran egg, 

 only here the groove never extends round the whole circle to 

 enclose a definite yolk-plug, but, as in Le pi dos ire n, shortens 

 up, flattening out at each end. The examination of sections 

 shows that here as in Lepidosiren the invagination groove 

 is at its first appearance distinctly within the coarsely-yolked 

 portion of the egg. 



The general features of gastrulatiou closely resemble those 

 in Lep idosiren, and it is therefore not necessary to describe 

 them in detail. I give, however, figures illustrating three 

 successive stages (PI. 2, figs, vi, viii ; and PL 3, fig. xii). By 

 compai'ison of fig. vi with fig. viii, the vertical axis being- 

 marked by the position of the segmentation cavity, it will 

 be readily seen how important a part is played by overgrowth 

 of the blastopore lip. The orientation of the egg during 

 these stages is rendered simpler than it is in Lepidosiren 

 by the segmentation cavity retaining its original relations 

 much longer. 



At the close of gastrulatiou the appearance of the egg is 

 practically identical with that of Lepidosiren. I notice, 

 hoAvever, that very frequently an egg of Protopterus at this 

 stage assumes an ellipsoidal form, with the blastopore either 

 at one end or somewhat ventral to this. In Lepidosiren 

 only pathological or unfertilised eggs assume an ellipsoidal 

 shape. 



As regards the further points of development treated of in 

 this paper, there do not appear to be any noteworthy differ- 

 ences between what occurs in Protopterus and what has 

 been described for Lepidosiren. 



1 The Protopterus egg very frequently passes tlirough a stage identical 

 ill appearance willi the stage in the development of Triton figured by 0. 

 llertwig in ' Jen. Zeits.,' Bd. xv, Taf. xii, fig. 1. 



