SUMMARY The normal behaviour pattern of Bufo regularis while moulting is described. The frequency of moulting has been determined in various conditions. At 20° C. these toads moult once every four to seven days. The frequency of moulting is not influenced by size, age or feeding, nor does there appear to be any difference in this regard between the sexes; any seasonal variation is slight. The frequency of moulting is greater at higher temperatures. Abrupt changes of temperature do not upset the moulting rhythm. At 25° C. less than an hour before moulting the toads pale markedly. The return to normal coloration is slower, taking more than four hours. The frequency of moulting is higher in toads kept in constant light than in those in constant darkness. In conditions of alternating light and dark there is a well marked preference for moulting during the hours of illumination at 25° and 30° C., but at 20° C. the effect is abolished. It is suggested that light can trigger the events which lead to the shedding of the skin.

In the estuary of the Kowie River in the Eastern Cape Province there occur two amphibious grapsoid crabs, Sesarma catenata Ort. and Cyc/ograpsus punctatus M. Edw. They live together in many places, commonly inhabiting the same burrows in the muddy banks of the river. The present exploratory study of these two species has been undertaken to enhance our knowledge of their biology as well as our understanding of the relations between these two very similar animals which live in such close proximity one to another. THE HABITAT The Kowie River empties into the sea at Port Alfred, and is broad, winding and shallow. The tidal limit lies 13 miles from the mouth and over most of this length extensive, gently sloping mudbanks are left exposed at low tide. The level of mean high tide is marked by a low salting cliff which is surmounted with vegetation. At Port Alfred itself the river runs between steep, stony, artificial dykes and on either side lie lagoons (Fig. 1). The lagoons on the East Bank (1, 2 and 3) are almost completely cut off from the river although an exchange of water does take place via seepage points in the dyke. The two western lagoons (4 and 5) are fully tidal. Large areas of the intertidal zone in the estuary are colonised by the tall, coarse marsh grass Spartina capensis Nees (S. stricta Roth.). This usually disappears about the level of High Water Neaps (HWN), to be replaced by a zone of typical salt marsh plants, dominated by Arthrocnemum, especially A. pillansii Moss, which has long stems, prostrate and woody at the base and terminating in erect green succulent tips. With the Arthrocnemum there may be mingled Spartina and Triglochin bulbosum L., particularly in low wet situations, and towards High Water Springs (HWS) Chenolea diffusa Thunb. A short distance below HWS Limonium scabrum (Thunb.) O.K. appears and spreads upwards, presently to give way to grasses, shrubs and trees. The zonation of plants on the banks of four of the five lagoons is very much the same as that along the river banks. The banks of Lagoon 4 (known locally as Little Beach) are sandy and devoid of vegetation. The two lagoons which lie furthest from the sea (3 and 5)contain masses of drifted algae, in particular the slender, branched brown alga Graci/aria verrucosa (Huds.

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