1. Figure 6.1 Osmotic challenges of amphibians and reptiles in saltwater, freshwater, and on land. In saltwater, the animal is hyposmotic compared to its environment, and because its internal ion concentration is less than that of the surrounding environment (internal < external), water moves outward. In freshwater, the animal is hyperosmotic to its environment, and the greater internal ion concentration (internal > external) causes water to move inward. On land, the animal is a container of water and ions, but because the animal is not in an aqueous environment, internal fluctuations in ionic balance result from water loss to the relatively drier environment. The animal actually has much higher ion concentrations (internal > external) than surrounding air, and if ionic concentrations reach high levels, as they do in some desert reptiles, ion transfer can occur via salt glands, usually in the nasal or lacrimal region.

2. Figure 6.2 Model depicting how transfer of water occurs in cells based on a freshwater system. Water moves by the process of osmosis across the semipermeable membrane of the cell. The direction of water movement depends upon ionic gradients. If ion concentrations are higher inside the cell than outside (as in this example), then water moves in to balance concentration of ions. Semipermeable membranes do not allow all molecules to pass through. Rather, some do and some do not. In addition, cells have the capability to actively transport molecules across membranes. Amphibians and reptiles use a variety of behavioral and physiological mechanisms to maintain water and ionic balance because few natural environments are isotonic with their body fluids.

3. Figure 6.3 Diagrammatic representation of the functional kidney in amphibians and reptiles (see text for differences). Solid circles and the heavy line represent the reduction in osmotic concentration of urine for an amphibian. The line would be lower for a reptile.Adapted in part from Withers, 1992.

4. Figure 6.4 Photo of Anaxyrus punctatus (Bufonidae) on glass showing the ventral water absorption patch. (L. J. Vitt and J. P. Caldwell)

5. Figure 6.5 Water-conserving posture in the hylid frog Hyla chrysoscelis. The posture minimizes surface area exposed, thus reducing evaporative water loss through the skin. (J. P. Caldwell)

6. Figure 6.6 Typical posture of frog absorbing water from surface. The frog (Chiasmocleis albopunctata; Microhylidae) maximizes contact of the ventral body surface with the damp substrate. (J. P. Caldwell)

7. Figure 6.7 Eleutherodactylus coqui uses different postures to regulate water loss. The chin-down posture with legs underneath the body minimizes water loss. Water loss is greatest during bouts of calling by males when the greatest amount of skin surface area is exposed. Adapted from Pough et al., 1983.

8. Figure 6.8 Phyllomedusa sauvagii (Hylidae) spreads lipids from lipid glands in the skin by a series of stereotyped movements using the feet. Arrows indicate direction of foot movement. Adapted from Blaylock et al., 1976.

9. Figure 6.9 Phyllomedusa hypochondrialis (Hylidae), a common frog in semiarid and savanna areas of Brazil, has the ability to reduce water loss considerably more than other Phyllomedusa species by waxing its skin when active and exposing the maximum amount of its small body (upper). During dry season, these frogs minimize water loss by minimizing surface area exposed. The frog in the lower panel is just beginning to emerge from a nearly balled-up state. It was found under a dry pile of vegetation at the peak of the dry season with several others. The skin surface was dry, and it took the frog nearly 10 minutes to come out of an apparent state of torpor. (J. P. Caldwell and L. J. Vitt)

10. Figure 6.10 The hylid frog Litoria novaehollandiae (Hylidae), encased in its cocoon, emerges after a rainstorm and begins to eat the cocoon. The cocoon consists of retained layers of shed skin. (S. J. Richards)

11. Figure 6.11 Photomicrograph showing 39 layers of stratum corneum forming the cocoon of the South American frog, Lepidobatrachus llanensis (Ceratophryidae). (R. Ruibal)

12. Figure 6.12 Scale microstructure in the two desert lizards Moloch horridus (Agamidae: A and B) and Phrynosoma cornutum (Phrynosomatinae: C and D). The medial surface of ventral scale epidermis (&beta1;-layer) is shown at two magnifications for each species, showing the interior bracing support of each scale and the scale-defining interconnections of scale hinges. Hinge joints (hj), deep portions of scale hinges that spread laterally, form a continuously connected surface. The epidermis is ruptured in B (medial side of &beta1;-layer) showing Oberhäutchen (ob) cover on walls of the scale hinge. The &beta1;-level epidermis in P. cornutum (D) shows surface pitting on the different levels of the hinge joint.

13. Figure 6.13 Schematic summary of the mechanism for cutaneous water collecting, transport, and drinking in Moloch horridus (A) and Phrynosoma cornutum (B). Arrows indicate directional movement of water. C through E are generalized models of the morphology of the water transport system in the two lizards. In C and D, narrow passageways below each scale expand into scale hinge joints. Water moves through the channels and collects in the scale hinges, which are interconnected (D). The scale hinge-joint channel system consists of a continuous floor of channels, all directed so that water ultimately flows to the corner of the lizard's mouth. Adapted from Sherbrooke et al., 2007.

14. Figure 6.14 Rates of evaporative water loss (EWL) are lower for individual geckos (Coleonyx variegatus) when they are aggregated in groups of two or three in retreats than they are when geckos are alone in retreats. Adapted from Lancaster et al., 2006.

15. Figure 6.15 The desert tortoise, Gopherus agassizii (Testudinidae), either drinks from natural depressions or constructs shallow water-catchment basins in the desert floor following periodic rainstorms (Medica, et al., 1980). (P. A. Medica; photo not included in published paper)

16. Figure 6.16 Concentration of plasma solutes remains stable (homeostasis) in desert tortoises as long as urine stored in the bladder is hyposmotic to plasma. When solute concentration of the plasma reaches that of the urine (isosmotic), solute concentrations increase in both (anhomeostasis). Data from two populations are included (IV = Ivanpah Valley; DTNA = Desert Tortoise Natural Area, both in the Mojave Desert). Adapted from Peterson, 1996.

17. Figure 6.17 Longitudinal section through a tadpole, showing the placement of the internal gills beneath the operculum.Adapted from Viertel and Richter, 1999.

18. Figure 6.18 Direct-developing young of the hylid frog Gastrotheca cornuta (Amphignathodontidae). Offspring develop in the dorsal pouch of the female, and oxygen diffuses from the female across the thin, bell-shaped gills of the froglet. Adapted from Duellman and Trueb, 1986.

19. Figure 6.19 Adaptive types of salamander larvae, or in some cases, paedotypic adults. Adapted from Duellman and Trueb, 1986.

20. Figure 6.20 Cutaneous exchange of gases in amphibians and reptiles. Open bars indicate uptake of oxygen; shaded bars indicate excretion of carbon dioxide. Values represent the percent of total gas exchange occurring through the skin. Adapted from Kardong, 1995.

21. Figure 6.21 Plethodontid salamanders, like this Plethodon angusticlavius, have no lungs. All respiration occurs across other skin surfaces. Consequently, all live in wet or moist habitats, most are secretive and/or nocturnal, and most are small in body size. (L.J. Vitt)

22. Figure 6.22 The Titicaca frog, Telmatobius coleus (Ceratophryidae), lives at great depths in Lake Titicaca and does not surface to breathe. The large folds of skin greatly increase the surface area of the skin, facilitating cutaneous respiration. (V. H. Hutchison)

23. Figure 6.23 Respiration in a frog. Oxygenated air is taken into the buccal cavity through the nares. Deoxygenated air in the lungs is rapidly expelled and does not mix with the air in the buccal cavity. Elevation of the buccal cavity (the buccal pump) forces the new air into the lungs. The glottis is then closed to hold the oxygenated air in the lungs, and the remaining air in the buccal cavity is expired by further elevation of the buccal cavity. Adapted from Withers, 1992.

24. Figure 6.24 Mean volume of erythrocytes decreases with increasing elevation in several frog species. Shaded circles are bufonids (originally reported as in the genus Bufo, now in the genera Duttaphrynus and Rhinella), open circles are Telmatobius (Ceratophryidae), and closed circles represent much earlier data from 22 anuran species in eight genera from Chile. Dashed polygons enclose data for bufonids and species of Telmatobius. Adapted from Navas and Chauí-Berlinck, 2007.