448 



THE NERVOUS SYSTEM. 



Even in the Crayfish the anterior or thalamic central gray 

 matter exhibits a cavity which extends into the procerebron, 

 giving it a vesicular character (Fig. 55, 2, x}. Moreover, it is 

 connected with a small and very remarkable cavity (Fig. 55, 2, q) 

 which one is almost tempted to compare with the hypophysis 

 of the vertebrate brain. I have at present been unable to in- 

 vestigate this curious organ more fully, and I have seen nothing 

 like it in any insect. 



The Supra-cesophageal Nerve Centres of the Cockroach (Blatta 



2. 



1 H.. 55. /. A. lateral section through the base of the brain of a Crayfish (Astacn: 

 fliiriatilis) : a, olfactory ganglion; < , iophageal connective; <r, cms ; in, 

 mesocerebron ; 0, optic peduncle ; ///, thalamon ; y, ascending fibres. 



2. A. more highly magnified section nearer the ventral surface of the ganglia : 

 cl, procerebral vesicle ; .v, ascending fibres ; </, ventricular cavity. The anterior 

 part of the ventricular cavity, containing a fan-shaped group of cells is seen 

 between the two bundles of ascending fibres. The other references as in /. 



orientalis) closely resemble those of the Crustacea. The 

 principal points of distinction are the smaller size of the 

 thalamic lobes, the far greater development of the meso- 

 cerebron and corpora fungiformia, and the transference of the 

 origin of the optic peduncle to the mesocerebron. Only a small 

 portion of it arises in Insects from the thalamic lobes ; but a 

 bundle of fibres can, so far as I know, always be traced on the 

 anterior surface of the optic peduncle into the thalamon. The 

 procerebron, although still very obscure, is lobulatcd, and the 



