PRESIDENTIAL ADDRESS. 33 



In mangrove swamps are numerous air breathers, which 

 are immersed frequently, yet do not venture beyond the 

 farthest reach of the sea, these include the slug Onchidium, 

 the snails Salinator and Ophicardelns. In the tropics this 

 amphibious fauna multiplies and includes fish in the case 

 of two species of Periopthalmus, Crustacea as Ccenobita 

 spinosa 1 and TJca, mollusca as Ceritliidea, Melaraphe and 

 Truncatella. Indeed migration from the sea to the shore, 

 or from salt water to fresh, is easier and more frequent in 

 a warm climate than in a cold one. 2 On Funafuti I found 

 Nerita plicata packed together in crevices of the rocks 

 far above high tide mark, behaving like a terrestrial rather 

 than a marine animal. 3 



All over the world the molluscan family Littorinidse, are 

 pioneers in emergence from the sea. Pelseneer describes 

 how the gill plume of a European species is shortened and 

 broadened to form an incipient lung. 4 Quoy and Gaimard, 5 

 observed that the ctenidium of Littorina angulifera had 

 shrunk from disuse in consequence of living more in the 

 air than in the water. 



A correlation between the station on the beach, and 

 embryonic life of different species is traced by Mr. W. M. 

 Tattersall, 6 as follows: — "Of the four British species of 

 Littorina, L. litorea is exposed only at low spring tides, and 

 is freed as a trochosphere, later becoming a veliger ; L. 

 obtusata is generally exposed at ordinary low water, and 

 is freed as a veliger ; L. rudis is exposed during the greater 

 part of the day, and is viviparous; L. neritoides lives 

 between the high water of springs and neaps and is also 



1 McCulloch, B,ec. Aust. Mus., vii, 1909, p. 303, pi. 88. 

 8 Origine des Animaux <T eau douce, Pelseneer, Bull. Acad. Roy. Belg. 

 1905, p. 724. 



3 Mem. Aust. Mus., iii, 1899, p. 409. 



* Pelseneer, Mollusca, 1906, p. 104. 



6 Quoy and Gaimard, Zool. Astrolabe, ii, 1833, p. 476. 



6 Tattersall, Nature, vol. lxxix, 1909, p. 478. 



C— May 5, 1915. 



