E. T. NEWTON ON PREPARING A MODEL OF AN INSECT^ BRAIN. 151 



backwards along the upper surface of the alimentary canal. Below 

 and behind the large commissures (cm) pass to the lower ganglia (lb), 

 and, being long in the Mole-cricket, the two pairs of ganglia are well 

 separated. In some insects they are much closer together. 



FIG. 1. — Brain of Mole-cricket, after Dietl. — ub, upper division of 

 the brain, or supra-oesophageal ganglia ; lb, lower division of brain, or in- 

 fra oesophageal ganglia; cm, commissures between upper and lower divi- 

 sions of brain; x, a cross-band of fibres peculiar to mole-cricket and 

 some other insects; an, antennaiy nerve ; op, optic ganglion; o, ocelli ; fg, 

 frontal ganglion of stomato-gastric nerve ; 1, 2, 3, nerves to mouth organs. 



From the lower pair of ganglia the nerves are given off which 

 supply the mouth appendages. The researches of Faivre, in 1857 

 (" Du Cerveaux des Dytisque dans ses rapports avec la locomotion." 

 " Ann. d. Sci. Naturelles. Zool." tome 8, p. 245) seem to show that 

 the power of co-ordinating the movements of the body is lodged in 

 the infra-cesophageal ganglia, and, therefore, it is not without reason 

 that some authors regard these as a part of the brain. What 

 follows in this communication refers only to the supra-cesophageal 

 ganglia, or, as I should prefer to call them, the upper division of the 

 brain. 



The general arrangement of the internal structures will, perhaps, 

 be best understood by reference to the figure given by Leydig, of the 

 brain of Formica rufa (Fig. 2.) ("Tafeln zur Vergleichenden 

 Anatomie," 1864, t. 8, fig. 4). Upon each side there is a large 

 central ovoid mass (pi), which has been termed, the primary lobe, 

 and this abuts in the middle line upon its fellow of the opposite 

 side, while the optic nerve, with its ganglion (op), is given off from 



