ANATOMY OF THE NERVE CENTRES. 469 
used, to a far greater extent than any of the other nerve- 
elements. 
The Antennal Nerve arises partly from the glomeruli and 
partly from the adjacent cortical substance in which its fibres 
can be traced into large stellate nerve cells. In the Cricket 
and many other insects two pairs of antennal nerves have 
been described—the large sensory nerve and a smaller motor- 
nerve, which supplies the muscles of the antenna. They are, 
perhaps, united into a single trunk in the Blow-fly. Possibly 
the nerve-fibres, which arise directly from the large stellate 
cells, are motor in function. 
The Optic Ganglion.—This term has been applied with different 
limitations. Viallanes includes under it all the nervous struc- 
tures between the inner extremities of the great rods of the 
compound eye and the hemispheres of the brain, but Berger 
[178], Ciccacio,* Bellonci, and Cuccati, as I think, correctly 
limit the use of the term to those parts included under it in the 
following description, naming the remaining structures the 
retina ; whilst Hickson} proposes to call the whole the retina. 
The optic ganglia of the Blow-fly differ but slightly from the 
same structures in the Insecta generally ; these are very similar 
‘to the corresponding parts in the Decapod Crustacea. 
I shall distinguish and describe the following: (1) The optic 
peduncle ; (2) the inner medulla ; (3) the outer medulla; and 
(4) the cortex. The relations of these parts will be most easily 
understood by a reference to Fig. 61. The remaining struc- 
tures, included by Viallanes as a portion of the optic ganglion, 
are my optic nerve and retina. 
1. The Optic Peduncle is frequently termed the optic nerve. 
If the term optic nerve is to be used in the Arthropoda, it 
certainly is inappropriate for the designation of this structure, 
which unites the optic ganglion and the cerebron. In order to 
be consistent, if the optic peduncle is to be termed the optic 
nerve, the optic ganglion should be termed the retina, as 
Hickson has done. To do so appears to me to be an un- 
* Mem. d. Accad. d. Sc. Bologna, tom. vi., 1884. 
+ Quart. Journ. Microsc. Sc., vol. xxv., 1885. 
