Tooth enamel is actually about the thickness of an egg shell, while gums are merely paper-thin.
On environmental questions, I see a situation where amateurs could became a vast data collection army, measuring all kinds of things -- thickness of birds' eggs, magnetic field fluctuations.
In fact, when the thicknesses of the egg envelopes were compared, the egg envelopes of euteleosts tended to be thicker than those of otophysans [ 26, 30].
Conclusions were unchanged when analysing punctures per unit surface area and taking shell thickness of the experimental egg and clutch membership into account (egg identity effect: F2,86 = 4.72, p = 0.011; shell thickness effect: F1,25 = 0.01, p = 0.93).
Egg identity (host, control or experimental) and shell thickness of the experimental egg were modelled as fixed effects, and clutch membership (and thus honeyguide laying event) as a random effect.
However, the thickness of the fertilized egg EC is not significantly reduced during the expansion, partially because of the discharge of stored EC proteins from the cortical granules and their incorporation into the expanding egg coat.
It might perhaps also provide an additional cue of prior parasitism if it reveals the greater shell thickness of another parasitic egg (table 1), although thickened eggshells could also be a defence against multiple parasitism as suggested for other egg-puncturing brood parasites such as cowbirds and Clamator cuckoos [ 7].
The variations could be due to sensitivity to UV irradiation from species to species and could be explained by differences in the thickness, composition, and optical qualities of egg chorion, egg size and shape, and the relative position of the female pronucleus (Myers et al. [1995]).
The lining changes in thickness during the menstrual cycle, being thickest during the period of egg release from the ovaries (see ovulation).
