THE 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 [237], 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 

 retinulse. 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 retiijal 

 nerve terminals of the Scorpion, and in so v me of their figures 

 there are structures which certainly bear a 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 simikrity of structure between the 

 rhabdomes of, say, Tipula as represented by Grenacher and 

 of the retinae of Scorpions represented (Ungrammatically by 



