524 THE Si:. \SF.S AM) SEXSORY ORGANS. 



Lankester and Bourne must be deceptive. In many of the 

 figures given by the last-named authors the 'yellow bodies' 

 in the retina do not appear to be normal structures, and from 

 what I have myself seen in many preparations bleached with 

 nitrous acid are, I believe, artificial products resulting from 

 the action of the acid upon the proteid of the circulating fluid. 

 Nothing can be well less like a normal structure than the 

 irregular masses of structureless material shown in their figures. 



I have little doubt as to the similarity of the pre-retinal 

 lamellae of simple eyes and the basilar membranes of compound 

 eyes, and I am quite convinced that in both the simple and 

 compound eyes all the parts on the inner side of these mem- 

 branes are developed as outgrowths from the central nervous 

 system. 



On the Structure of the Great Rods. Grenadier's figures in- 

 dicate that the great rods vary extremely in structure in a 

 most puzzling manner in different Arthropods, and anyone 

 who has worked at transverse sections of these organs knows 

 how variable the appearances are which they exhibit, even in 

 the same species, in different sections. Compare, for example, 

 the figures given by Grenacher [222, Figs. 125, 126] with those 

 by Lankester and Bourne [229, Figs. 20-26] of the so-called 

 retinulae of Limulus. These are typical representations of 

 gigantic rhabdomes. I have no reason to distrust the figures 

 given by either, because I have frequently observed equal 

 discrepancies in transverse sections of rhabdomes prepared 

 by slightly different methods from insects of the same 

 species. 



In 1882, on examining the eye of a Plume Moth, Ptcrophorns, 

 after dissociating the elements of the dioptron with needles 

 in normal saline solution, I was surprised to find that the 

 great rods presented appearances which had not been pre- 

 viously observed. Each great rod consisted of an ovoid 

 transparent body (PI. XXXVIII., Fig. $ rh] ; this rapidly un- 

 derwent changes of form evidently due to the escape of fluid 

 from its interior, and ultimately split up into a number of 

 empty tubules. These were neither more nor less than the 



