>02 



HARDWICKE'S SCIENCE- GO S SIP. 



tion of it given above. On the ventral cord, how. 

 ever, the ganglia, and the main lateral branches, 

 there appears to be another and thicker envelope 

 surrounding the neurilemirjx at some distance, and 

 showing traces of longitudinal muscular fibrillae. 

 Between these two coats the terminations of the 

 tracheal tubes, as already noticed, pass, and seem 

 to ramify upon the surface of the inner one ; a 

 trachea on each side entering together with the 

 main lateral nervous branches at every ganglion. 



The usual double form of the ventral cord is, in 

 this insect, replaced by a single one ; whether this 

 has ^arisen from the coalescence of two originally 

 distinct cords I do not know, bat I have frequently 

 observed both in the larva and in the imago, a slight 

 separation or split in the cord immediately above 

 each ganglion, which gives me the impression that 

 this might have been the case. It is furnished with 

 twelve ganglia, two of which belong to the head, 

 three to the thoracic, and seven to the abdominal 

 segments. Of the two cephalic ganglia, which toge- 

 ther form the brain, one lies above the oesophagus 

 and the other beneath it, the two being connected 

 by [two large nervous trunks, which conuect the 

 upper with the lower, and embrace the oesophagus 

 between them. Speaking of these, Burmeister 

 says:* "I consider that which lies above as the 

 cerebrum of the higher animals, the lower one, on 

 the contrary, as the cerebellum, and indeed because, 

 as in the higher animals, the nerves of the superior 

 organs of the senses, viz. of the eye, spring from 

 the upper ganglion, and from the lower one, on the 

 contrary, the nerves cf the mandibles, lips, and 

 tongue proceed." I shall adopt, therefore, this 

 nomenclature, and regard these two ganglia as the 

 cerebrum and cerebellum respectively. The cere- 

 brum consists of two ganglia or lobes, connected 

 by a nervous cord, lying transversely across the 

 oesophagus, and, so far as I have been able to trace 

 them, the nerves which pass from it are as follows. 

 A nerve originates from the anterior portion of 

 each lobe and passes to the antenna?., giving off two 

 branches, one of which arches over the frontal 

 sympathetic ganglion, the other I have not been 

 able to trace. Close to this- another nerve arises, 

 and proceeds to I he antennal imaginal disc, where, 

 I believe, it divides, one branch entering the future 

 antenna of the imago, and the other, after passing 

 along the lower border of the disc, again divides 

 into two branches, one of which I have not traced, 

 and the other forms a second arch in front of the 

 first, joining its fellow of the opposite side in the 

 central line of the oesophagus, immediately in front 

 of the frontal sympathetic gangliou. From the 

 point of junction a central nerve runs down the 

 oesophagus, and either joins the frontal ganglion or 

 passes beneath it, I am not quite sure which. A 



* Shuckhard's Translation, p. 2/2. 



T fork is thus formed in front of the latter, which 

 will be recognized in my drawing. From these 

 branches others proceed to the labrum, and others 

 again connect them with the first-named arches of 

 the antennal nerves of the larva. Exterior to these 

 nerves arise the much thicker ones which proceed 

 to the optic imaginal discs, and form the optic 

 nerves of the imago. 



The cerebellum has three pairs of nerves, as 

 follows : — a nerve arises from its anterior border on 

 each side, and ends in a small ganglion near the 

 base of the maxilla; another arises near this, and 

 shortly divides ; one branch passes backwards, and 

 is distributed to the large muscles of the mandibles ; 

 the other passes forwards and again divides, one 

 branch proceeding to the base of the mandibles, and 

 the other I have not traced. The third pair of 

 nerves arise from the ventral surface of the cere- 

 bellum, and passing forward they divide, one branch 

 on each side, proceeding to the muscles before re- 

 ferred to as connected with the salivary duct, and 

 the other terminating iu a small ganglion, one of 

 a pair situated immediately below the mouth, 

 behind the mentum. 



The three thoracic ganglia which follow the cere- 

 bellum send out each two pairs of nerves, one from 

 their superior and one from their inferior or ventral 

 surfaces ; the former are distributed to the muscles 

 of the segment, and the latter to the inferior ima-- 

 ginal discs, with, I think, a prolongation to the 

 corresponding superior one3 ; but of this I am not 

 quite certain. These are accompanied by the 

 tracheal branches proper to the ganglia. The 

 seven succeeding abdominal ganglia likewise send 

 out each two pairs of nerves, the homologues of 

 those last named, one directed forwards and the 

 other and larger pair directed backwards. Both 

 are distributed to the muscles of the segments 

 to which they belong. With respect to the latter, 

 I would observe that it almost immediately divides, 

 the branches embracing the longitudinal muscles 

 which flank the cord ; one branch is joined by the 

 trachea proper to the ganglion, and the other, after 

 passing under the diagonal and succeeding longitu- 

 dinal series of muscles, ends in a small ganglion, 

 which may be found in the centre of the spaces 

 between the conspicuous transverse muscles of the 

 lateral bands, whence again smaller ramifications 

 proceed to the longitudinal ones near the dorsal 

 vessel, &c. Many of these small branches— perhaps 

 all, if I could fairly see them— are accompanied by 

 minute tracheae; indeed the association of the tra- 

 cheal and nervous systems seems to me a feature 

 worthy of notice. The terminal ganglion of the 

 cord, in addition to the nerves above mentioned, 

 sends out two other large ones, which pass back, 

 ward to the muscles near the anus. It is to be 

 noticed that there are nine abdominal segments, 

 but only seven abdominal ganglia. Are the ganglia 



