CEREBRAL HOMOLOGIES. 



37 



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 commissures 



The "nervous cord" here signifies the central tracts — 

 ganglionic 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 " \. 



But the associated microscopical investigators and manipu- 

 lators, Burgess and Mason, found in the " entire brain " (my 

 ''fore brain," or " hsemoesophageal centres," a): — " 1. An 

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

 up of ' cortical cells '"§; 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- 

 mat ter"§. 



Remembering the transposition of the grey and white 

 neurine in diff'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 



* Packard, ' Second Eeport ' &c. p. 224. 

 t lb. p. 224. J lb,, p. 22(3 



§ lb. p. 227. 



