THE COMPOUND EVE. 521 
and the axial rod, when it consists of the united rodlets, a 
rhabdome, owing to the fluted structure it exhibits, paSdwoma 
signifying the fluting of a column. 
I take exception to the whole of Grenacher’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 Retinule 
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 retinulee, 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 Letween 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. 81 of his memoir Grenacher 
says, speaking of the eye of Tipula sp.: ‘On the inner side of 
the tender cuticular membrane on which the retinulz rest, the 
fibres of the optic nerve run’ [222, Fig. 44, ct]. There is no 
attempt to prove that these fibres enter the retinule or per- 
forate the cuticular membrane, nor do I think Grenacher has 
anywhere stated that he has himself traced the nerves into 
the retinula. 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- 
