20 Routes from the Sea 



Verwey, 1930) . It is apparent along the borders of coral reefs 

 (Stephenson, Stephenson, Handy, & Spender, 1931) and also along 

 those of fresh-water lakes (Forel, 1892-1904; Muttkowski, 1918). 



Migration from aquatic to land habitats takes place most readily 

 when the atmosphere alongshore is humid (Harms, 1929; Lusk, 

 1917) . The height which marine animals attain on beaches is 

 more or less directly related to humidity (Fischer, 1927) . Animals 

 that have taken up life on land have variable degrees of adjustment 

 to atmospheric humidity. Some absorb water; others lose water at 

 all temperatures, even when the air is saturated. Some animals 

 become dormant in low humidities; others are active at night (Lud- 

 wig, 1945) . On rocky shores marine crabs scamper in and out of 

 the ocean most often at night, during rains, or when spray dashes 

 high. In crevices animals can live higher than on exposed rock 

 surfaces, because they are somewhat sheltered from wave action 

 and desiccation. Along muddy beaches crabs and fishes wander 

 into the adjacent land vegetation and often dodge into burrows. 

 On clay and sand beaches animals commonly live in burrows and 

 emerge only when humidity is favorable. 



Air-breathing animals which take up residence between tides 

 must migrate inshore at intervals or be able to endure submergence 

 for several hours. Littoral mites can live for a couple of days under 

 water (King, 1914). Intertidal insects have air stored in their 

 tracheae, but also take advantage of small quantities of air which 

 remain in crevices when the tide covers the beach. 



On rocky coasts there are few or no plants at high-tide mark, but 

 barnacles often occur in great numbers (Allee, 1923, 1923a; Pearse, 

 1914, 1929, 1931). Some rock barnacles are so situated that they 

 are not covered by water except during the highest tides, which do 

 not occur every day. A barnacle is typical of rock-beach animals — 

 firmly attached; protected by a heavy calcareous covering against 

 desiccation, extreme changes in temperature, and the pounding of 



