452 THE NERVOUS SYSTEM, 
(Pl. XXVIII., 7, mx). On either side of the opening are the 
crura, and above it the great mass of the supra-cesophageal 
centres, which form by far the largest part of the brain. The 
Fic, 58.—A stereographic representation of a side view of the brain of the Blow-fly 
imago. (See description of Plate XXVIII.) The optic peduncle has been cut 
through close to the mesocerebron : me, external lobe of the mesocerebron ; ms, 
superior lobe of the mesocerebron. The other references as in Plate XXVIII. 
parts of the supra-cesophageal centres are the antennal 
ganglia, a a; the central nerve-masses or cerebron; the optic 
peduncles, 0s; and the optic cap, or the external medullary 
mass of the optic ganglion, oc. 
DEscRIPTION OF PLATE XXVIII. 
Stereographic figures of the brain of the Blow-fly imago. (These figures were con- 
structed in the following manner: a number of drawings were made from several 
series of serial sections by means of a camera lucida; every section was drawn to the 
same scale; from these a clay model was constructed, and the figures were taken 
from this model by means of a camera.) The external outline represents the 
surface of the gray matter, the shaded drawing represents the medullary reticular 
substance. Fig. 58 is a side view of the same model. 
Fic. 1.—The brain seen from in front. 
Fic. 2,—The ventral aspect of the same. 
a, antennal ganglion ; a’, antennal nerve ; ¢ ¢, cephalo-thoracic cord ; /, frontal 
lobe of the meso-cerebron; / e, external, and / 2, internal corpus fungiforme ; 
z, infra-cesophageal centre; 7 7, inferior lobe of the mesocerebron ; 72x, maxillary 
nerve ; 0, nerve to the ocelli; 0 5, optic peduncle ; 0 c, optic cap ; fA, pharyngeal 
nerve ; //, thalamon. 
