THE EYE AND OPTIC TRACT OF INSECTS. 
237 
crystalline cones, in 1864 Leydig was able to express a very 
strong opinion that the retinulse (Nervenfasern) are the nerve- 
end cells and “ dass man die Analoga nicht in den gewohn- 
lichen Nervenprimitivfasern der Wirbelthiere suchen darf, 
sondern einzig und allein in den Bacillis und Conis der Retina 
hoherer Thiere.” 
The same opinion was expressed in 1868 by Max Schultz 
(18), who at the close of his exceedingly careful and valuable 
work on the compound eyes of Crustacea and Insects, says 
that it is a proved fact that the retinulse (Sehstaben) are the 
end-organs of the optic nerves. 
In 1879 Dr. G-renacher, after a prolonged and laborious 
re-investigation of the whole subject, came to the same con- 
clusion, and for the first time introduced the term “ retinulse ” 
for the structures which are now almost universally known by 
that name. 
After the subject had thus been thoroughly investigated and 
re-investigated by such celebrated naturalists, and the results 
of such investigations had led to conclusions which in all 
important respects were identical, it might have been thought 
that the matter was definitely settled. However, a short paper 
was published last year in the ‘ Proc. Roy. Soc./ by Mr. Lowne 
(15), in which a view was put forward that the retinulse are not 
the nerve-end cells at all, but that the true retina is situated 
behind the basilar membrane. Lowne’s retina is situated in 
Musca in a position identical with my peri-opticon, and I have 
no doubt that he has mistaken the elements of this ganglion 
for cells, just as Carriere (3) did, and supposed that they 
corresponded with the retinal cells of other animals. But this 
view is perfectly untenable, for not only does anatomy teach 
us that the optic nerve-fibrils end in the retinulse, but morpho- 
logy teaches us that they are homologous with the nerve-end 
cells of the eyes of other animals, and the few physiological 
experiments that have been made also show that they are 
eminently adapted for light-perceiving purposes. 
If anything further were required to prove that the retinulse 
are homologous with visual nerve-end cells of other animals, it 
