ANATOMY OF THE NERVE 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 trabeculz 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 Cerebron.—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 (Pls. XXIX., XXX., and XXXIL., ¢ /). 
—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 (Pl. XXXIL., 
