GASTRULATION OF THE VERTEBRATES. 413 
between the blastopore of the Vertebrate (often only potential 
in mammals! and not identical with the opening that is called 
by that name in Sauropsids) and its primitive groove. A 
phylogenetic continuity has to be statuated between this oral 
slit of the Actinia and the peculiar spot (behind the so-called 
anterior lip of the blastopore) which on the Vertebrate 
embryonic shield gradually moves backwards and establishes 
in many cases an open communication between a portion of 
the Vertebrate intestine and the exterior. The primitive 
streak, however, the solid material that proliferates down- 
wards from the ectoderm, coalesces with the entoderm, and 
brings forth the notochord from its median (though really 
paired) portion and the somites from its lateral wings—this 
Fic. 5.—Gastrula stage of Torpedo. 
primitive streak can never be identified with a blastopore or 
primitive mouth, neither with the lips of the blastopore. 
For we have above attempted to demonstrate that in this 
primitive streak we encounter the material which, also in the 
Actinia, (1) proliferates downwards from the ectoderm and 
produces the stomodzeum, (2) coalesces with the entoderm, (3) is 
in direct continuity with those parts which are preparing to 
give rise to ccelomic pouches but are yet continuous with the 
primitive enteron. 
Certain prudent changes of nomenclature would perhaps 
1 An open blastopore has up to now only rarely been noticed in Mammals, 
In Erinaceus I have observed it quite clearly (*‘ Furchung und Keimblattbildung 
bei Tarsius,’ Pl. XII, figs. 8,9). Keibel (l.c. Taf. 24, figs. 46, 47) is less 
positive as far as the rabbit goes, so are Selenka (Taf. 17 and 18) for the opos- 
sum, and Bonnet (Anat. Hefte, Bd. 9, Taf. 32) for the dog. 
