No. 3.] DEVELOPMENT OF THE TOAD-FISH. 497 



A notched blastopore, at a distance behind the embryo, has 

 hitherto been unknown among teleosts. 



In rare cases a notch has been observed at the posterior end 

 of the embryo, in transitory stages of pelagic fish eggs. In 

 such cases the caudal lobe is divided as in Elasmobranch em- 

 bryos. Two instances have been reported by Agassiz and 

 Whitman, and one by Kingsley and Conn. Although due to 

 the same processes of growth, this notch cannot be the same 

 as that seen in the egg of the Elasmobranch or Batrachus. 



It should be mentioned that the germ ring is remarkably nar- 

 row as compared with that of other teleosts, especially pelagic 

 forms. This is due, probably, to the extension of the germ 

 ring over a larger yolk sphere. 



In Fig. I. c, the position of Kupffer's vesicle is unusual. 

 When first seen, it lies at the extreme posterior end of the 

 embryo, at the notch of the blastopore. In a later stage, Fig. 

 I. d, this vesicle is seen to lie a little in front of the hind end of 

 the embryo. It seems probable that the embryo has lengthened 

 somewhat backward. 



It is interesting in this connection to refer to some rare 

 appearances in the blastoderm of the chick. A marginal notch 

 in the blastoderm has been observed by Pander, Balfour, His, 

 Rauber, and others, while the extension of the primitive groove 

 through the area opaca to this notch has been seen by Dr. 

 Whitman and Dr. Bohm. 1 



In comparing the Elasmobranch and Avian embryos, Dr. 

 Whitman 2 says: "In the exceptional form of blastoderm 

 which I have described, the streak connecting the primitive 

 groove with the marginal notch may be considered analogous 

 to the linear streak of the Elasmobranch, while the marginal 

 notch corresponds to the anterior angle of the yolk blastopore." 



These exceptional forms seem to point to the same funda- 

 mental principle of embryonic formation in Elasmobranchs and 

 Aves. 



1 Archiv fur Anat. unci Phys., 1884, p. 14. Dr. T. H. Morgan has informed me 

 that he also has observed the notch and the extension backwards of the primitive 

 groove to it in the chick. 



2 Quart. Jour. Mic. Set., Vol. XXIII. New series, 1883. 



