444 THE NERVOUS SYSTEM. 
large 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, 7 and 2) show that the three pairs 
of central ganglia are united by three transverse commissures, 
which are separated from each other by small groups of nerve 
cells. 
These three primary divisions of the Arthropod supra-ceso- 
phageal centres have not hitherto received distinctive names ; 
Fic. 54.—Lateral sections through the brain of the Crayfish : 7. Just above the origin 
of the optic peduncle; 2, Near the upper limit of the mesocerebron. ¢ 2, com- 
missure of the thalamon; ¢ a, cesophageal connectives ; #7, anterior, and m', 
posterior reticular nucleus of the mesocerebron; m/, metacerebron ; 9, 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 meten- 
cephalon of Vertebrates, I propose to designate them as the 
thalamon (Fig. 54, th), the mesocerebron (m), and the meta- 
cerebron (mt) 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 
