Chapter 1, The Reptilian Spectacle - UWSpace - University of ...

having perhaps a more highly developed dermis and a thinner stratum corneum”. It is not clear what
constitutes a “more highly developed dermis,” nor is it clear if he found a multi-layered stratum
corneum as in snakes, but given the results presented in Chapter 4, it is possible that he did not.
Likewise, he made no explicit claim about the spectacle being vascularized, though later researchers
confirmed that it was (Lüdicke 1971; Mead 1976). Lüdicke, in his investigation of the ocular blood
supply of Gekko gecko, showed the meshwork to be somewhat radial and irregular in arrangement and
to exhibit a high degree of anastomosing. Notably, he also found the blood vessels to be smaller than
those of snakes, measuring 4-17 µm in diameter. It is unclear, however, how a 4 µm vessel can pass the
large nucleated erythrocytes of geckos, which are greater than 9 µm on the shortest dimension (Saint
Girons and Saint Girons 1969; Starostová et al. 2005). Given the vagueness of Ficalbi’s observations
on the gecko spectacle, its innervation has yet to be truly established.
Unlike snakes, the scales of most geckos are small, in some cases resembling tubercules, and
don’t overlap (Pianka and Vitt 2003). In these species, the size of the spectacle scale thus makes it by
far the largest of their integument, which, as in alethinophidian snakes, is just large enough to cover the
cornea of the eye but no larger, being bordered by the extra-brillar fringe. In one gekkonid genus,
Ptenopus, the extra-brillar fringes are hypertrophied, contain muscle fibers and are mobile, allowing
the fringes to incompletely cover and shield the spectacle (Smith 1939; Bellairs 1948). Interestingly,
this species burrows in dry sandy habitats (Haacke 1975), which has led Bellairs (1948) to suggest that
the extra-brillar “eyelids” (spectaclids? brillids?) protect the spectacle from abrasive sand and dust, a
curious arrangement given that the spectacle itself is typically considered to be protective against the
very same (see the section on Adaptive Significance below).
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