45 = 



THE NERVOUS S VST KM. 



(PI. XXVIII., /', mx). On either side of the opening are' the 

 crura, and above it the great mass of the supra-oesophageal 

 centres, which form by far the largest part of the brain. The 



FIG. 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 : i,\ external lobe of the mesocerebron ; rtis, 

 superior lobe of the mesocerebron. The other references as in Plate XXVIII. 



parts of the supra-oesophageal centres are the antennal 

 ganglia, a a ; the central nerve-masses or cerebron ; the optic 

 peduncles, o s ; and the optic cap, or the external medullary 

 mass of the optic ganglion, o c. 



DEM'KIl'lION OF 1'I.ATK XXVIII. 



Stereographic figures of the brain of the Blow-tly 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. 



FIG. I. The brain seen from in front. 



FIG. 2. The ventral aspect of the same. 



a, antennal ganglion ; a', antennal nerve ; c t, cephalo-thoracic cord ; _/, frontal 

 lobe of the meso-cercbron ; / e, external, and / ;', internal corpus fungiforme ; 

 i, infra-oesophageal centre; ;// /', inferior lobe of the mesocerebron ; tx, maxillary 

 nerve ; o, nerve to the ocelli ; o s, optic peduncle ; o t, optic cap ; ///, pharyngeal 

 nerve ; t/i, thalamon. 



