EYES AND SIGHT, 
101 
Optic nerve fibrils, which cross one another, as seen 
at n 0 (Fig. 44). This second ganglionic swelling is 
separated from the next, the opticon, by a tract of 
nerve fibrils, which partially decussate, and a few 
scattered nerve cells. Beyond this is the cerebral 
ganglion, separated from the opticon by a narrow 
constriction, which Berger ( 2 ) has pointed out to 
be the homologue of the optic nerve of the other 
arthropoda. The three optic ganglia, together with the 
cerebral ganglia, are surrounded by a sheath of very 
densely packed nerve cells, called by Leydig (95) 
Funktsuhstanz^ and found by him to consist of densely 
packed nucleated cells, connected together and having 
amongst them fine nerve fibrils. The cells are not so 
densely packed in a developing bee as they are in the 
adult, and are therefore more easily distinguished. 
The opticon consists of a very fine granular 
matrix, traversed throughout by a fine mesh work of 
minute fibrils, which tissue Hickson calls neiirospon- 
gium. The periopticon is composed of a number of 
cylindrical masses of neurospongium, arranged side 
by side, into which the nerve fibrils coming from the 
epiopticon, and divided into two or three fibrils, enter. 
These again sub-divide, and form the fibrillar mesh- 
work of the neurospongium. The nerve fibrils from 
these elements join the numerous nerve cells, which 
in turn furnish the fibrils which pass through the 
basilar membrane to supply the retinulse, as shown by 
Grenacher. Numerous tracheae are found running 
more or less parallel with the basilar membrane, and 
which spring from the tracheal trunks situated behind 
