104 Mr Stark on Two Species of Pholas. 



ed regarding the mode by which the Pholades make their per- 

 forations. 



The Pholades being incapable of moving from their place, 

 the young are dropped from the tube of the parent on the 

 surface of their native rock. How they are enabled to pene- 

 trate the rock, so as to secure themselves protection ; or how, 

 previously to having formed a cell, they adhere to the surface, 

 has not hitherto been explained. Rondeletius, like others of 

 the older naturalists, who believed in spontaneous generation, 

 supposed that the sea-water lodging in the pores of the rocks 

 might become, in process of time, Pholades ; * — a supposition 

 not more distant from truth than that which long afterwards 

 prevailed as to the Lepas anatifera being the young of a 

 species of goose ! Perhaps some glutinous matter, such as 

 fixes the byssus of the Mytili, may keep the fry of the Pho- 

 lades in their place till they have excavated a hole sufficient 

 to conceal themselves : but future observation, by those who 

 have the opportunity, will, there is little doubt, discover the 

 arrangement by which these animals are enabled to commence 

 their cells. 



The Pholades, it may be remarked, seem admirably con- 

 structed for the purposes of their existence, so far as these are 

 known. Possessing but a comparatively fragile shell, which 

 the least force would break, and, having no weapons of de- 

 fence against their aquatic enemies, Nature has furnished 

 them with the means of amply providing for this apparent de- 

 ficiency, by giving them an asylum in the solid rock. Having 

 formed their destined habitations, which they can never leave, 

 the rock is honeycombed by successive races till it falls in 

 pieces, and a new surface is exposed for new generations. 

 The tribes of Pholades on the different coasts are thus active 

 and powerful instruments in the disintegration of rocks. The 

 shale in which they occur at Joppa runs in parallel and alter- 

 nating strata with a coarse sandstone ; and while the uncon- 

 nected ridges of the sandstone still appear, rounded by the 

 weather, or hollowed into basins by the action of the waves, 

 the alternating beds of shale have nearly disappeared, through 

 the instrumentality of these powerful, though unseen agents. 



* Ronrtelet. Be Trstaceis, lib. i. p. 49. Lugd. 1555. 



