IN YERTEBEATBS AND INYEETEBRATES. 5 



The latest ueurotomist of the Arthropoda, for example, con- 

 cludes, emphatically, as follows : — " It should be remembered that 

 the word "brain" is applied to the compound (supracesophageal) 

 ganglion simply by courtesy and as a matter of convenience, as 

 it does not correspond to the brain of a vertebrate animal, the 

 brain of the horse or man being composed of several distinct pairs 

 of ganglia. Moreover, the brain and nervous cord of the fish or 

 man is fundamentally different, or not homologous with that of 

 the lower or invertebrate animals." " The nervous cord of the 

 insect consists of a chain of ganglia connected by nerves or com- 

 missures"*. 



The " nervous cord " here signifies the central tracts — gan- 

 glionic or otherwise — occupying in Invertebrates what is held 

 to be, and is described as, the "ventral region" of the body- 

 cavity. 



The structural phenomena cited in support of the foregoing 

 negation are : — " The entire brain of an insect is white, as are all 

 the ganglia "f; while " the spinal cord of the fish or man consists 

 of two kinds of substances or tissues, called "grey" and "white 

 substance" J. 



But the associated microscopical investigators and mani- 

 pulators, Burgess and Mason, found in the " entire brain " 

 (my "fore brain" or " hgemoesophageal centres," a): — "I. An 

 outer, slightly darker, usually pale greyish-white portion, made 

 up of ' cortical cells ' " J ; and " II. The medullary or inner part of 

 the brain consists of matter which remains white or unstained 

 after the preparation has remained thoroughly exposed to the 

 action of carmine. It consists of minute granules and interlacing 

 fibres. The latter often forms a fine irregular network enclosing 

 masses of finely granulated nerve-matter " §. 



Eemembering the transposition of the grey and white neurine 

 in difi'erent parts of the vertebrate neural axis, I cannot give the 

 value to a similar transposition in parts of the invertebrate neural 

 axis which Professor Packard assigns thereto. 



The eyes of the Cuttlefish are the homologues of those of the 

 Lump-fish, as are the optic nerves and the cerebral mass super- 

 added, in both, to the centre receiving the impressions of those 

 nerves. Such homology legitimately extends from Cephalopods 



* Packard, ' Second Keport ' &c., p. 224. t lb. p. 224. 



X Ib.-p. 226. § ^*- P- 227. 



