The Victorian naturalist . ation becomes apparent). Fertiliza-tion must be in the body of the snail,and the developing embryo must beprotected until it is able to withstand the rigours of the environment. The methods of protection againstdesiccation in land molluscs are mainlybehavioural. The snails seek out dampsheltered places under rocks or logsor buried in the ground, and onlyemerge when the conditions are cooland wet and the evaporation rate ispractically nil. Thus snails emergemainly at night or only on wet, over-cast days. Aestivation In hot dry weather the snails go intoa period of dor
The Victorian naturalist . ation becomes apparent). Fertiliza-tion must be in the body of the snail,and the developing embryo must beprotected until it is able to withstand the rigours of the environment. The methods of protection againstdesiccation in land molluscs are mainlybehavioural. The snails seek out dampsheltered places under rocks or logsor buried in the ground, and onlyemerge when the conditions are cooland wet and the evaporation rate ispractically nil. Thus snails emergemainly at night or only on wet, over-cast days. Aestivation In hot dry weather the snails go intoa period of dormancy or aestivation,very similar in some ways to the hiber-nation of some vertebrates in coldclimates. When conditions start to becomeunfavourable for the snail, hot and drywith little moisture, it is forced intoplaces of shelter away from the ex-tremes. (One or two species do not dothis and they will be discussed below.) The snails either seal themselvesdown to a hard surface or secretecalcareous membranes over the shell. Figure 1. Ventral view of desert snailshowing position of a series of epiphragms. * Curator of Invertebrates,National Museum of Victoria. 128 Vict. Nat. Vol. 93 aperture. These membranes are calledepiphragms and in some desert snailsseveral epiphragms are secreted (). The membranes or seahng sub-stance is a special mucus-type sub-stance which hardens in air to an im-pervious layer. These protective measures are de-signed to minimize water loss. Internalbody processes such as respiration,heart-rate, excretion and others areslowed right down to practically noth-ing, probably under hormone control. Some desert snails have the abilityto remain in aestivation for years, onlycoming back to life when sufficientwater is present to dissolve the epi-phragm and provide the initial sti-mulus to the animal. This facility ofdesert snails to undergo extendedaestivation is a special adaptation todesert life. Ordinary garden snails can only sur-vive aestivation for a fe
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