444 



THE NERVOUS SYSTEM. 



lar-^e fasciculus of fibrils, corresponding with the peduncle and 

 trabecula of the insect brain. This terminates in the cortex 

 and penetrates a very remarkable group of small round cells, 

 which I shall term the corpus fungiforme, as I regard it as the 

 homologue of the corpora fungiformia of insects. 



Lateral sections (Fig. 54, / and 2) show that the three pairs 

 of central ganglia are united by three transverse commissures, 

 which arc separated from each other by small groups of nerve 

 cells. 



These three primary divisions of the Arthropod supra-ceso- 

 phagcal centres have not hitherto received distinctive names ; 



l-'i>:. 54. Lateral sections through the brain of the Crayfish : /. Just above the origin 

 i 'I the optic peduncle ; 2. Near the upper limit of the mesocerebron. t t/i, com- 

 missure of the thalamon ; < <r, oesophageal connectives ; m, anterior, and ///', 

 posterior reticular nucleus of the mesocerebron; nit, im-Mcerebron ; o, optic 

 peduncle ; ///, thalamic lobes. 



as they exist in all Insects, and probably in all Crustaceans, 

 some distinctive names should be applied to them. As these 

 three groups of ganglia are apparently developed from three 

 vesicles (in the Diptera), and are in many respects analogous 

 to the thalamencephalon, the mesencephalon and rneten- 

 cephalon of Vertebrates, I propose to designate them as the 

 thalamon (Fig. 54, ///), the mesocerebron (;;;), and the meta- 

 cerebron (nit) respectively. These terms have the advantage 

 of being easily remembered, and can, I think, give rise to no 

 confusion ; even if future researches should not confirm the 

 view I hold, that they are really the representatives of the 



