164 PATTEN. [Vou. IL. 
matter to develop the inverted cells at the expense of the 
upright ones. The degenerated retinal cells could then be 
transformed into the tapetal matrix, the retinal cells producing 
tapetal scales instead of rods, as the inverted retinal cells in 
Chauliodes give rise to the inner lens. If this be true, then 
the tapetal slit might be compared to the median furrow in the 
retinas of Acilius. 
A probable instance of such a method of inversion is found 
in Pecten, whose inverted rods I derived from the outer wall of 
an optic vesicle, by supposing that partially inverted and upright 
rods existed at the same time; eye V. of Acilius furnishes 
us with a needed example of such an eye. Moreover, in Pecten 
there is evidence that the inner wall was derived from a retina, 
the retinophore of which were transformed into the argentea or 
reflector, and the ganglion-cells into the red pigment layer. 
Such a transformation of the optic vesicle of Spiders would 
harmonize with Bertkau’s description of the tapetal eyes, or 
“ Nebenaugen.’ The anatomy of the non-tapetal ones, as far 
as known, would lead one to believe the retina is composed of 
upright cells, while embryology says they are inverted.1 
In the earliest stages of Acilius, the eyes are composed of 
several sensory pits, each with its cuticular thickening and nerve. 
It is possible that in the Arachnids the numerous nerve bundles 
supplying the eyes, such as figured by Grenacher for Lycosa 
(Pl. III., Fig. 22), might owe their existence to the fact that 
these eyes also were formed by the fusion of several sense 
organs. 
We might change the eyes of Acilius into the Aranean type 
by suppressing the eyes of the third segment and inverting the 
retinas in all but the large posterior pair. The latter would 
then become the “ Hauptaugen” of Spiders, and the smaller 
ones with inverted retinas the “ Vebenaugen.” 
The failure to form, either by speculation or observation, an 
adequate notion of the origin of the retina in Arthropods has 
long stood in the way of a satisfactory explanation of the various 
structural forms these eyes assume. It was not possible to treat 
the subject comprehensively and systematically while still in 
1Jt is difficult to understand Bertkau’s statement that his observations confirm 
those of Grenacher. There certainly is a great difference between his drawings of 
the tapetal eyes and those of Grenacher. 
