80 Reviews — B. B. Woodward's Life of the Mollusca. 



Thus one is led to consider where the mollusc began to take up his 

 abode, and it is suggested that the tidal zone was in all probability 

 the cradle of the race. " From the shore-line the various members 

 betook themselves to probably deeper and deeper water on the one 

 hand, but also, though perhaps more tentatively and gradually, to 

 fluviatile and terrestrial conditions on the other." Thus we see the 

 early human infant begins his marine efforts by 'paddling', and it is 

 long before he attempts deeper water or, like the Argonauts of old, 

 risks a pelagic adventure far from land. From the earliest times 

 soft-bodied (molluscous) animals have doubtless been attractive to 

 their fellows as well as to the early nomads who lived upon the waifs 

 and strays which the waves cast up upon the shore. The shell of all 

 tj'pes, univalve, bivalve, and multivalve, were a necessity to these 

 early molluscs. "Primarily among the inhabitants of a rough fore- 

 shore the massive strength of the shell is noticeable, the object being 

 of course to withstand the battering action of the waves and hard 

 substances, like stones, cast up by them" (p. 103). 



The limpets with their tent-shaped shells afford an example of an 

 excellent protective form of covering for a surf-dweller on rocks. 

 The Trochus, Turbos, and Neritas among spiral forms have usually 

 stout shells and often also a shelly operculum or door to their houses. 

 Such forms as Littorina, Fur'pura, Nassa, Pterocera, Tiirhinella, and 

 Strombus require much sea hammering to break their shells. In 

 deeper water, however, where no surf breaks, the thick heavy shell 

 of the Gastropods ceases to be of service, and the inhabitants adopt 

 a much thinner and lighter covering (p. 104). 



Among the bivalves (Pelecypoda) also the shore frequenters often 

 have very stout and convex shells, like the Giant Clam {Tridacna) 

 and the Hippoptis, and can withstand the full beat of the ocean 

 waves ; so too could the Rudistes among the fossil reef-building 

 molluscs. But "most of the Bivalves, as a matter of fact, do not 

 live in exposed situations, but burrow more or less deeply into soft 

 sand or silt". Those that do not penetrate to any depth below the 

 surface, nor live in deep water beyond the reach of ground-swells, 

 such as the Cockle, Cardimn, the Veneridse, etc., are often disturbed 

 by storms and thrown up alive upon the beach. Their activity, 

 however, frequently enables them to got back (by walking with their 

 foot) into their briny home, where they quickly buiy themselves 

 once more in the sand. 



All sections of the group except the bivalves have a distinctive 

 feeding organ, the 'radula'. It occupies the same position in the 

 mouth as does the tongue in the higher animals, and consists of 

 a series of recurved teeth, formed of dense chitine, attached in 

 transverse rows to a membrane of the same substance. " The number 

 of teeth in each transverse row varies from one in certain sea-slugs 

 to upwards of two or three hundred as in the ' top shells ' and their 

 allies {Trochis, Haliotis, etc.)" (p. 11). The whelk has about 250, 

 a big limpet 2,000, the periwinkle 3,500, the common garden snail 

 15,000, and the big grey slug 26,800. As in the higher animals, 

 " the form of the teeth are some index to the diet of the animals, the 

 purely herbivorous having short broad-pointed teeth, the carnivorous 



