162 PATTEN. [Vot. II. 
Locy maintained that the ocelli of Spiders were formed of in- 
vaginated vesicles, the outer walls of which became the retinas. 
Mark, in discussing the various theories that had been ad- 
vanced to account for the origin of the retina and its method of 
formation, says, p. 54, that Locy’s observations ‘seem adequate 
to settle these conflicting views— so far at least as regards 
the spider-like type.’ Great stress is laid upon the inversion 
of the retina in Spiders, for he says (p. 54), “The inversion of the 
retina proper is a fact of broader significance than would at first 
sight appear, and it affords a satisfactory explanation of some 
of the points in the anatomy and histology of simple eyes which 
have been so earnestly discussed during the past few years.” 
And a little farther on he intimates that it is doubtful if any 
Monomeniscus Arthropod eyes contain upright retinas. In fact, 
the main purpose of his paper is to show that the Arthropod 
ocelli are constructed on the “ Spider-like type,” that is; of three 
layers, the inverted middle one forming the retina. Wherever 
in the ocelli of Arachnids, Myriapods, and Insects there is evi- 
dence of a post-retinal layer and a “dentigen” with a retina 
between, Professor Mark would infer that the eye originated as 
in Spiders, and he seems to have found evidence of one or more 
of these structures in the eyes of Myriapods and Scorpions and 
in the larval and frontal ocelli of Insects. 
In the present state of our knowledge, the larval and frontal 
ocelli of Insects cannot be made to fit this theory; certainly 
not in Acilius and Vespa, the two cases to which Professor 
Mark gives especial attention. In Vespa, I have shown since 
his paper was published that the frontal ocelli were derived 
from open-mouthed pits, the inner wall of which gave rise to 
the retina. 
The eyes of Myriapods are so much like those of Coleopterous 
larvee that there is every reason to suppose they develop in the 
same way. 
It would not be safe to conclude from Parker’s observations 
that the retina of the median eyes of Scorpions is inverted, 
since they do not extend to sufficiently young stages. But, 
according to his observations, the lateral eyes are single-layered, 
and consequently the retinal cells are upright. Professor Mark 
regards the retinal cells in the median eyes as inverted, and 
since the rods and nerve fibres do not indicate any such inver- 
