PRESIDENTIAL ADDRESS. 55 



upon this open coast is heavier and more forceful than 

 that seen on most European shores. A striking instance 

 of its power is recorded by Mr. O. A. Siissmilch, 1 who 

 described and illustrated a block of sandstone at Bondi, 20 

 feet loDg, 16 feet broad, and 10 feet high, estimated to 

 weigh 235 tons, which was capsized, dragged 50 yards and 

 lifted 10 feet during a gale. 



Marine organisms which have to endure such fury as 

 tossed this block at Bondi, undergo special adaptation. In 

 the first place they are skilled at taking cover, appreciating 

 to the full the shelter afforded by a tuft of weed, a crack 

 or a projecting ledge of rock. Without such shelter exist- 

 ence would for most be here impossible. 



Evolution has conducted various inhabitants of the surf- 

 zone by epharmonic convergence to the same tent-like shape. 

 Just as a similar mode of defence has imposed a superficial 

 resemblance on the hedgehog and the Echidna, so resistance 

 in the sea has moulded many different stocks to the same 

 external form. Though of unlike origin and widely different 

 in anatomical features, the gasteropods Emarginula, 

 Siphonaria, and Acmaea have now assumed a shell hardly 

 to be distinguished on the outside from the real limpet. 

 Travelling an even longer road, the barnacle has changed 

 from a mobile crustacean to a fixed limpet-like cone. For 

 example, Catophragmus polymerus (fig. 18), common in 

 the surf zone and distinguished by its whorls of scales, like 

 a daisy's petals, shows the last stage of transition from a 

 stalked to a sessile barnacle, as if it were a telescoped 

 Scapellum. The limpet itself is doubtless the last term of 

 a series of trochoidal, multispiral gasteropoda. 



For this low cone or tent shape is that on which rushing 

 water takes the least grasp, the stream shearing off from 

 its evasive sides. As a further mechanical advantage, the 



1 This Journal, xlvi, 1912, pp. 155 - 158, pis. iv, v, vi. 



