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, 7) 
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 
Fic. 55.—v. A lateral section through the base of the brain of a Crayfish (Astacus 
fluviatilis): a, olfactory ganglion; ¢ @, cesophageal connective ; cv, crus; mm, 
mesocerebron ; 0, optic peduncle; //, thalamon ; y, ascending fibres, 
2. A more highly magnified section nearer the ventral surface of the ganglia : 
cl, procerebral vesicle ; «, ascending fibres 5 9, 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 s. 
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 lobulated, and the 
