THE COMPOUND EYE. 521 



and the axial rod, when it consists of the united rodlets, a 

 rhabdome, owing to the fluted structure it exhibits, pa/3Bu>^a 

 signifying the fluting of a column. 



I take exception to the whole of Grenadier's conclusions. In 

 the first place, I maintain that there is not the smallest evidence 

 that nerve-fibres enter either the pigment cells of the sheath or 

 the sheathing cells. In the second place, I maintain that there 

 is not the slightest homology or analogy between Grenacher's 

 Stabchen and Rhabdomes and the retinal cells of the simple 

 eye. And, in the third place, I consider that the structure of 

 the great rods has been incorrectly interpreted by Grenacher. 



I shall discuss these three points in the above order. 



On the Supposed Innervation of the Great Rods, or Retinulae 

 of Grenacher. If Grenacher has traced the optic nerve-fibres 

 into the cells of the great rods, I would ask why he has not 

 represented this relation in his figures. So important a point 

 would. certainly, I think, have been figured if he had ever traced 

 the fibres into the retinulse, as he terms them, yet I fail to find 

 a single figure showing this relation satisfactorily ; and the 

 great majority of his figures indicate a distinct line of demarca- 

 tion between the great rods and the nervous structures beneath 

 the basilar membrane, which in the majority of cases Grenacher 

 has not figured at all. On p. Si of his memoir Grenacher 

 says, speaking of the eye of Tipula sp. : ' On the inner side of 

 the tender cuticular membrane on which the retinulas rest, the 

 fibres of the optic nerve run ' [222, Fig. 44, ct]. There is no 

 attempt to prove that these fibres enter the retinulse or per- 

 forate the cuticular membrane, nor do I think Grenacher has 

 anywhere stated that he has himself traced the nerves into 

 the retinulae. He contents himself with a general statement, 

 and nowhere attempts to bring distinct proofs in support 



of it. 



It appears to me evident that Grenacher regarded the 

 classical opinion, that the optic nerve terminates in some part 

 of the great rod, as a correct one, and troubled himself no 

 further about it. He perceived that its terminations could not 

 possibly be in the cuticular rhabdome, and regarded the pig- 



