304 Prof. Owen on the Answerable Divisions of the 
Generalizing such particular questions and accepting the 
current replies, he would be justified in affirming that there 
was no homology between the vascular centres or systems of 
Vertebrates and Invertebrates. 
Thesameconclusion, on the above assumption of their respec- 
tive backs and bellies, affects another and, in this relation, more 
important organic system. Homology would be repudiated 
as between the myelencephalon of Vertebrates and the centres 
of the nervous system in Articulates. In the former the 
“brain,” and, as in Amphiorus, a more constant part, viz. 
the ‘* spinal marrow,” are held to be on the ‘ dorsal ”’ aspect 
of the body; in Articulates the ganglionic chord, functioning 
as “ spinal marrow,” is held to be on the “ ventral” aspect of 
the body. They may be, accordingly, “ analogous” or 
‘homodynamous,” but are not answerable parts in the 
“homologous ”’ sense. 
An exception is indeed made by some zootomists in favour 
of one portion of the neural axis :—“ The central nervous 
system of the Vertebrata is to be regarded as representing the 
superior or cerebral ganglia cf Invertebrata” *,—that 1s, as 
being homologous with such ganglia and with their coalesced 
and developed condition in the Cephalopod; although, im 
fact, the part described as “brain” in such Invertebrate 
represents no more than the part of the brain in Vertebrates 
which is in connexion with the senses of sight and smell. 
The ground, in short, on which such conclusions are based 
is simply that of the relative position to a part or aspect of 
the body as this may be carried by the animal during loco- 
motion. 
But before testing the value of such support of the conclu- 
sion, as it affects the question of homology, I may refer to 
the degree in which it checks or paralyzes another and higher 
biological line of thought. Gegenbaur, for example, finds 
it ‘‘ quite impossible to derive the spinal chord from it” f, 
that is, to derive phylogenetically the continuous or more 
or less uniform myelon of Vertebrates from the ganglionic 
myelon of Arthropods and Annulates. I by no means think 
that a study of their developmental relations is to be aban- 
doned in despair, the answerable aspects being rightly deter- 
mined. But, before moving further on this line, I may remark 
that enlargements at the points where nerves communicate with 
* Gegenbaur, ‘ Elements of Comparative Anatomy,’ Ray Lankester’s 
edition, 8vo, 1878, p. 501. Prof. Packard, more consistently, repudiates 
even this degree of homology (see his ‘Second Report of the U.S, Ento- 
mological Commission,’ 1880, p. 224). 
+ Op, cit. 2b. 
