ANATOMY OF THE NERVE CENTRES. 46? 



situated behind the corpus centrale ; its base rests on the 

 floor of the central cavity ; the metacerebron is immediately 

 behind it, chiefly represented by a transverse commissure. 

 The apex of this ganglion is situated in the posterior part of 

 the longitudinal fissure, between the internal corpora fungi- 

 formia ; its axis is traversed by numerous fibres, which form 

 the roots of the nerve to the ocelli. 



The Nerve of the Ocelli. This nerve is single in the Blow-fly ; 

 it emerges from the apex of the pyramidal ganglion as a single 

 cord, which divides into three branches immediately beneath 

 the three ocelli, and ends in the retinae of these organs. 



In the Cricket there are three distinct ocellary nerves two 

 lateral and a single median nerve. 



According to Viallanes [185, Mem. 5], the median ocellary 

 nerve in the Cricket arises by two roots, one on either side. 

 These roots join the deep origins of the lateral nerves, and 

 may be traced in part at least to a small internal tubercle, 

 which projects from the inner surface of the posterior part of 

 the hemisphere. The nerve to the ocelli in the Blow-fly has, I 

 believe, a similar connection with the hemisphere, although 

 many of its fibres come from the nerve-cells of the pyramidal 

 ganglion. 



d. The Sensory Ganglia. 



The Olfactory or Antennal Ganglia are a pair of spheroidal 

 ganglia, which project from the front of the brain. They are 

 united with each other by a strong commissure. Each 

 ganglion is connected with the corresponding hemisphere by a 

 peduncle, consisting of four principal bundles of fibres. 



1. Bellonci's Bundle traverses the hemisphere from before 

 backwards, and terminates in the gray matter between and 

 below the corpora fungiformia. These fibres were first seen 

 by Bellonci [183] in the Diptera. 



2. The Trabecular Bundle (PL XXIX., Fig. 2) decussates 

 with its fellow in the middle line, and joins the trabecula of the 

 opposite side. 



