184 BULLETIN OF THE 
Graber (’79, p. 59) raised the question whether the lens consists of 
only the normal cuticular layers thickened, or contains additional layers. 
This is a question upon which evidence is not easily obtainable, for 
it deals with layers which in the lens may be of considerable thickness 
and yet remain so thin as to be almost imperceptible in the indifferent 
euticula. The condition of the lens in young individuals offers some 
evidence. About the time a young scorpion leaves the mother’s back, the 
indifferent cuticula appears to consist conclusively of what in later stages 
corresponds to the external hyaline layer. Careful search has failed to 
show any subjacent cuticula, and yet in the region of the lens a very per- 
ceptible layer of stainable cuticula is visible. This seems to indicate 
that the lentigen has the power of producing cuticula independently of 
that produced by the indifferent hypodermis. Admitting this, it seems 
probable that of the many lamelle in the lens some may be peculiar to 
the lens itself and unrepresented in the adjacent cuticula. 
The separation of the retina and lentigen, as discovered by Grenacher, 
was further emphasized by Graber’s discovery (79, pp. 64-67) of a 
limiting membrane (“ praeretinale Zwischenlamella”) between them. 
This preretinal membrane, as Graber showed, is continuous with the 
“sclera” and the basement membrane of the hypodermis. The explana- 
tion of these structures which is offered by the formation of the eye from 
a hypodermal sac, has already been discussed by Mark (’87, p. 71). He 
has claimed that the sclera is the basement membrane of the post-retinal 
layer, and that the preretinal membrane is the fused basement membranes 
of the lentigen and retina. The explanation given in the case of the 
infolded eyes of spiders applies equally well to the median eyes in 
scorpions. 
As to the nature of the basement membrane, especially in the region of 
the sclera and preretinal membrane, two opposing theories have been 
advanced. Graber (’79, pp. 63, 64) maintains that the basement mem- 
brane including the sclera is cuticular, not cellular, and as its matrix he 
claims cells whose nuclei were found both by Grenacher (’79, p. 60, fig. 
34) and himself (’79, p. 64, fig. 18). -For the preretinal membrane 
Graber (79, pp. 64, 65) also claims a cuticular nature and states that it 
contains no nuclei. Lankester and Bourne (’83, p. 189) describe the 
ommateal capsule or sclera as laminate and devoid of nuclei. Mark (’87, 
p. 71) believes that the basement membrane with its modifications is a 
cuticula derived from the basal ends of the hypodermal cells. 
Opposed to these views Schimkewitsch (’84, pp. 8, 9, 11, 12) main- 
tains that the basement membrane and its modifications are connective 
