1885.] Affinities of Annelids to Vertebrates. 773 
blastopore area of the gastrula—the area opposite the upper end 
(summit) of the gastrula and in a plane at right angles to the 
chief axis of the gastrula,and along this ventral surface or blas- 
topore area the nerve-cord is developed. In the vertebrate, on 
the contrary, the blastopore closes in a small area representing 
the posterior end of the adult and entirely behind the nervous 
system, corresponding in part to the anus in position. The blas- 
topore area being thus the hind end of the adult, the ventral sur- 
face of the adult is formed from one side of the gastrula while 
the nerve-cord develops upon the opposite side of the gastrula in 
a position more nearly parallel with the chief axis of the 
gastrula. 
In an annelid, then, the ventral surface with the nerve-cord cor- 
respond to the original lower or blastopore surface of the gas- 
trula, and the mouth represents the anterior end of the blasto- 
pore. In a vertebrate the ventral surface corresponds to a side of 
the gastrula, while the surface homologous to the annelid’s ven- 
tral surface is found represented in the vertebrate merely by the 
anal region, this being the blastopore-area of the gastrula; the 
mouth in the vertebrate is a new structure formed remote from 
the area of the blastopore, and not at all comparable to the annelid 
mouth except in function. 
Figs. 8 and 9, copied from Goette’s work, will serve to illus- 
trate this comparison of the two groups. 
VM i CMM 
nn 
Fig. 8. Fig. 9. 
G. 8.—Dia ye of annelid according to Goette. D, dorsal, V, ventral surface ; 
Me apen A, an Fic. ọ9.—Diagram of reiterate according to Goette. D, 
dorsal, V, ‘ventral ieee? i mouth; A, anus. 
The preceding statements may serve to indicate the chief views 
upon the subject, showing how much difference prevails in the - 
-hypotheses advanced to solve the important morphological prob- 
lem of the exact affinities of the annelids and vertebrates, and at 
the same time indicating, perhaps, a tendency among those who 
have recently investigated the embryology of the annelids to 
