YHE COMPOUND EYE. 523 
Patten has described and figured in Mantis ; I only say I have 
never seen the same thing in any insect. What I maintain 
is that, even if it is admitted to be a real structure, Patten 
does not adduce the slightest evidence of its nervous nature, 
and the entire absence of end organs precludes the conclusion 
that it is a retina. 
Hickson [287], in a paper which was intended as a refutation 
of my views published in 1884, describes what he terms a 
neurospongial network, and traces this into Grenacher’s 
retinula. Anything more unlike nerve terminations cannot be 
conceived. His figures are good, and represent the connective 
reticulum and tracheal vessels only; all traces of any repre- 
sentation of nerve endings are absent in most of his figures, and 
his view, like Patten’s, is too improbable to require serious 
investigation. 
The above is the whole of the evidence on which the received 
view rests. No author has satisfactorily represented the nerve 
terminating in the dioptron, and no two authors who have 
imagined such terminals agree in the details they describe. 
On the Supposed Homology of the Great Rods and the Retina of 
the Simple Eye—Anyone who will take the trouble to compare 
the figures given by Grenacher of the retina of the simple eye 
with those of the rhabdomes of the compound eye will be at 
once struck with the slight similarity which they exhibit. 
Lankester and Bourne have, however, represented the retinal 
nerve terminals of the Scorpion, and in sqme of their figures 
there are structures which certainly beara striking resemblance 
to the rhabdomes of a compound eye. I have not had the 
opportunity of examining their specimens, but in some noctuid 
Moths almost identical structures exist in my retinal layer, 
which are certainly not anything like rhabdomes, although in 
specimens bleached with nitrous acid they approximate very 
closely in appearance to those represented by Lankester and 
Bourne. ‘Therefore, unless my retina and the great rods are 
homologous, this apparent simikarity of structure between the 
thabdomes of, say, Tipula as represented by Grenacher and 
of the retinze of Scorpions represented diagrammatically by 
