166 PATTEN. [Vot. II. 
But it cannot be denied that I foresaw in my paper on the “ Eyes 
of Molluscs and Arthropods”’ not only the origin of the retina 
and its method of formation, but, to a great extent, that of the 
optic ganglion as well. The observations on the development 
of Vespa and Acilius now furnish a substantial support for the 
theoretical views advanced in that paper, and this confirmation 
does not lose any of its value in consideration of the inversion of 
the retina in the tapetal eyes of Spiders, for that can most readily 
be explained, as already shown, by referring to the condition in 
eyes V. and VI. of Acilius; or by the fact that Reichenbach’s 
and Kingsley’s observations point to the conclusion that the 
sensory part of the convex eye is inverted, for in both instances 
the misconception undoubtedly arises from a confusion of gan- 
glionic and optic invaginations; and finally the inference lies 
close at hand that the supposed inversion of the retina in the 
eyes of Scorpions and in the non-tapetal ones of Spiders is due 
to a similar confusion of the two invaginations. 
Convex Eyre.—In my paper on the “Eyes of Vespa,” an 
attempt was made to throw some light in the phylogeny of the 
“convex eye.” It seemed to me that a solution of the problem 
might be obtained by explaining its double nature; for as 
shown by the embryology of Vespa and by the permanent 
condition in such forms as the Libelluliden, Ephemeriden, 
Gyrinnus, Astacus, Phronima, Schizopods, and others, it is prob- 
ably composed throughout the Arthropods of a distinct ventral 
and dorsal part. 
I attempted to explain this double condition by supposing 
that it was a modified larval ocellus like the posterior dorsal 
one of Acilius and Dytiscus, which I maintained was also 
composed of a dorsal and ventral part: the latter was the ocellus 
‘proper; the former, an appendage whose structure and general 
appearance indicated that it was a secondary and younger part 
subsequently added to the ocellus; and it was maintained that if 
such an ocellus developed into the compound eye, a needed expla- 
nation would then be furnished of its double nature. But there 
was no evidence to show that the posterior ocellus with its dorsal 
appendage really did develop into the convex eye. I deter- 
mined to obtain such evidence, if possible, by studying the 
history of the eye of Acilius during the larval and pupal stages. 
But all my efforts to obtain pupze were unsuccessful. I have 
