ANATOMY OF THE NERTE CENTRES. 455 



the internal medullary mass (optic peduncle), and^internally with 

 its fellow, in front and behind. The cavity enclosed by these 

 lobes contains the median protocerebron ' (my procerebron 

 and corpus centrale). ' It presents in its antero-lateral region 

 a deep fissure (the lateral fissure), which extends from' (the 

 cavity containing) ' the corpus centrale to the]' (front of the) 

 * inferior lobe.' Thus, the lobes of the cerebron consist of 

 two parts, separated by the lateral fissure (sillon lateral), an 

 anterior and a posterior, of which the latter is far the larger. 

 Viallanes' external lobe of the middle protocerebron in the 

 Cricket appears to me to correspond with my thalamic lobe, 

 and both lie within the lateral fissure. Thus, in the main 

 points there is apparently but little difference between the 

 hemispheres of the Cricket and the Blow-fly; and a comparison 

 of the manner in which the trabeculse are related to the lateral 

 fissure, at their anterior extremities, confirms the closeness 

 with which these parts agree in the two insects. 



Morphology of the Lobes of the Csrebron. Although in the 

 above description of the hemispheres I have regarded all the 

 lobes except the thalamic lobes as belonging to the meso- 

 cerebron, I am by no means convinced that the frontal lobes 

 are part of it. In separating the thalamic lobes, and regarding 

 them as part of the thalamon, I have been chiefly guided by 

 the manner in which they are related with the optic peduncles, 

 and with the procerebral lobes. The union of these masses 

 with the basal part of the mesocerebron is so intimate that, 

 until more definite information can be attained as to their 

 manner of development, this must be regarded as a provisional 

 view ; it is one, however, which commends itself very strongly 

 to my mind. 



The Procerebral Lobes (Pis. XXIX., XXX., and XXXIL, c /). 

 These are very largely developed in the Blow-fly, and con- 

 sist of two lobulated masses of medullary substance. They 

 are situated in the anterior part of the cavity of the cerebron, 

 and are concealed by the frontal lobes and antennal ganglia, 

 so that they cannot be seen externally. These lobes are 

 united with each other by a transverse commissure (PI. XXXIL, 



