The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash—free dry weight (°=6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three measures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for UTA stansburiana, with first and older breeders exhibiting the same effort. Sceloporus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selective pressure determining reproductive effort, and that reproductive effort may not be positively correlated with age in all species.

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Summary 1. Lipids deposited on the surface or embedded within the cuticle of terrestrial plants and arthropods are primarily responsible for the observed low rates of water loss through the cuticle. 2. These lipids are a mixture of long‐chain compounds which include hydrocarbons (saturated, unsaturated, branched), wax esters, free fatty acids, alcohols, ketones, aldehydes, and cyclic compounds. 3. The cuticle of both plants and arthropods is a continuous, non‐cellular multilayered membrane which overlies the epidermal cells. 4. In arthropods, horizontal division of the cuticle into layers is clearly visible. In plants, the layers comprising the cuticle are not sharply demarcated. 5. The substance responsible for the structural integrity of the plant cuticle (cutin) is composed of cross‐esterified fatty acids; structural integrity in arthropod cuticle is provided by a chitin‐protein complex. 6. Cuticular lipids are probably formed near the surface in both plants and arthropods; however, specific sites of synthesis are known for only a few species and little is known about their transport from these sites to the surface. The elaborate pore canal and wax canal system of arthropod cuticle is absent from plants. 7. The physical structure and arrangement of the lipid deposits on the cuticular surface that are so important in controlling water movement depend on both quantity and chemical composition, and are, in turn, specific to each species in relation to its environment. 8. Different lipid components are not equally efficient in reducing transpiration. Maximum waterproofing effectiveness is provided by long‐chain, saturated, non‐polar molecules containing few methyl branches. 9. Plants and arthropods can, within genetic constraints, alter the composition of their cuticular waxes to improve impermeability when conditions require increased water conservation. 10. None of the models proposed to explain the change in arthropod cuticular permeability which occurs at a species‐specific temperature (‘transition temperature’) in many species is supported by the experimental data now available.

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