, except for one cocooned N. aquilonius with a higher concentration of 394·pg·ml -1 . For both species, AVT showed no relationship with plasma osmolality over the lower range of plasma osmolalities but was appreciably increased at the highest osmolality recorded. This study provides the first evidence that cocoon formation following burrowing is not obligatory in species that are capable of doing so, but that cocoon formation occurs when soil water conditions are more desiccating than for non-cocooned frogs.

No abstract

Ocular arrangement and visual acuity were examined in Lycosa leuckartii Thorell 1870 (Araneae: Lycosidae), using histological techniques. Major structural and functional features of the visual system, including external and internal ocular organizations, resolution, sensitivity, focal lengths and the field of view, were characterized for each eye. Lycosa leuckartii had a large developmental investment in a specialized visual system with high visual acuity. The field of view extended 360° and displayed the potential for good depth perception. Anterior eyes showed average focal lengths (AL eyes 230.88 pm, AM eyes 276.84 pm), while the posterior eyes far exceeded them (PL eyes 499.26 pm, PM eyes 675.35 pm). Resolution of the anterior eyes was comparable to records in the literature for other lycosids (inter-receptor angle AL eyes 2.45°, AM eyes 1.85°), while the resolution of the posterior eyes was higher (PL eyes 0.78°, PM eyes 0.67°). Sensitivity of the lens (/-numbers) was highest in the secondary eyes and was close to some of the highest reported for Araneae (/-numbers PM eyes 0.58), but when receptor diameters were included in estimates, S-numbers were similar or lower than closely related species (PL eyes 17.5 pm", PM eyes 17.6 pm"). There is a clear distinction in organization and function between the posterior and anterior eyes of L. leuckartii. The posterior eyes suit long-range predator and prey detection, while the anterior eyes are best for distance judgment and prey capture.

Arenophryne rotunda is a small (2-8 g) terrestrial frog that inhabits the coastal sand dunes of central Western Australia. While sand burrowing is a strategy employed by many frog species inhabiting Australia's semi-arid and arid zones, A. rotunda is unique among burrowing species because it lives independently of free water and can be found nocturnally active on the dune surface for relatively extended periods. Consequently, we examined the physiological factors that enable this unique frog to maintain water balance. A. rotunda was not found to have any special adaptation to reduce EWL (being equivalent to a free water surface) or rehydrate from water (having the lowest rehydration rate measured for 15 Western Australian frog species), but it was able to maintain water balance in sand of very low moisture (1-2%). Frogs excavated in the field were in dune sand of 4.4% moisture content, as a consequence of recent rain, which was more than adequate for these frogs to maintain water balance as reflected by their low plasma and urine osmotic concentrations. We suggest that in dry periods of the year, A. rotunda can achieve positive water balance by cutaneous water uptake by burrowing deeper into the substrate to where the percent water content is greater than 1.5%.

No abstract