Brain in Vertebrates and Invertebrates. 305 
or pass from the Vertebrate myelon are many in some fishes 
(e.g. Zrigla), and they are present, though in smaller number, 
in the short myelon of Orthagoriscus*; and, further, that 
the researches ot the microscopist and the experiments of the 
physiologist have led to the conclusion that the seemingly 
continuous and uninterrupted tracts of the spinal chord of 
Vertebrates are due to a coalescence through superadded or 
interposed neurine of as many ganglionic centres receptive 
of neural impressions, sensory or motory, which essentially 
are as distinct, or in as special topical relations to the nerves 
proceeding from or returning to such centres, as are the 
physically seemingly separate centres in the so-called “ ventral 
ganglionic chords” of Invertebrates T. 
To what indeed are the grounds of such above-cited judg- 
ments on the important homological questions at issue reduced 
when subjected to anatomical analysis ? 
One of the several ganglionic enlargements of the knotted 
chord and centre of the nervous system in Invertebrates is 
propounded as the homologue of the brain in Vertebrates ; 
and [ accept such homology, but only in the restricted sense or 
degree above noted. Jor [ hold that the neural centres in rela- 
tion to the sensations and motions of the tongue, jaws, and other 
parts of the mouth in Invertebrates, which centres are in direct 
communication through continuous “crura”’ or chords with 
the so-called “brain,” are physiologically answerable to the 
parts of the brain with like nerves and functions in Verte- 
brates. 
That there are parts of the Vertebrate myelencephalon which 
correspond with, are certainly analogous to, and, I believe, 
homologous with, such parts in Invertebrates, I have elsewhere 
endeavoured to demonstrate |. The sole ground for rejecting 
such homology, or for its restriction to a part only of the brain 
of Invertebrates, is a different relation of the gullet to the 
prot- and metencephalous masses in Vertebrates and Inverte- 
brates. The space dividing the fore brain (“ protencephalon ” 
of Vertebrates, ‘“‘ supercesophageal ganglion” of Invertebrates) 
from the hind brain (“ epencephalon ” of Vertebrates, “ sub- 
esophageal ganglion” of Invertebrates) is so reduced in 
Cephalopods, especially the Dibranchiates, that the recogni- 
tion of their homology with the corresponding divisions of the 
brain in Vertebrates becomes obvious. 
The intervening space is scarcely, if at all, less in the 
* ¢ Anatomy of Vertebrates,’ vol. i. 1866, p, 271, 
t Newport, Phil. Trans. 1848, p. 243. 
t ‘Aspects of the Body in Vertebrates and Invertebrates,’ 8yo, 1833, 
