CEREBEAL HOMOLOGIES. 



33 



backward, and might be called the " ganglions " of smell, 

 sight, taste, and hearing. 



These several sense-centres are not in contact with one 

 another in all Vertebrates. The olfactory ganglia are con- 

 nected by long cords with the optic ganglia in many fishes 

 (Cyprinoids e.y.*). The tracts intercommunicating with the 

 trigeminal lobes recall the corresponding ones known as 

 " oesophageal cords " in Mollusks and Insects. Short and 

 thick in all V ertebrates are the tracts of the macromyelon, or 

 *' medulla oblonga," connecting the gustatory with the audi- 

 tory nerve-centres ; but all such centres, with superadded 

 masses, are reckoned parts of the " brain." 



The condition which affects the length and tenuity of the 

 tracts connecting the optic (diagram, fig. 11, a f) with the 

 oral (ib. b) nerve-centres in Invertebrates is the course of the 

 alimentary canal (ib. c I) neuradf, along the interspace be- 

 tween the foremost and the next neural centres. 



The elongated liomologues of th'e' vertebrate "crura cere- 

 bri '' are termed by Lyonnet, with sound homological views, 

 " conduits de la moelle epiniere " { ; by later anatomists, 

 rejecting his views, " oesophageal cords " or " commissures." 



In illustration of the present suggestions of the homologies 

 in question, I propose to take, from the group of Arthropods, 

 the nervous system of the Locust§. 



The first, commonly foremost neural mass (fig. 11, a), 



* Tom. cit. p. 275, figs. 177, 178. 



t Ibid. p. 276, fig. 172 (Chimcera). See also ante, fig. 3. 

 + ' Traite anatomique de la Chenille qui ronge le bois du Saule,' 4to, 

 1762. 



§ As represented in Caloptenus femur-rubrum, 0. spretus, and 0. bi- 

 vittatus, by the exemplary dissections and microscopic sections of MM. 

 Burgess and Mason, described and figured by Prof. Packard in the 

 ' Second Eeport of the U.S. Entomological Commission,' 1880, pp. 223- 

 242, pis. ix.-xv. 



D 



