found on the Sea-coast near Edinburgh 4S7 



The Pholades being incapable of moving from their place, 

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

 face of their native rock. How they are enabled to penetrate 

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

 ly to having formed a cell, they adhere to the surface, has not 

 hitherto been explained. RONDELETIUS, like others of the ol- 

 der naturalists, who believed in spontaneous generation, sup- 

 posed 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 

 M ytili, may keep the fry of the Pholades in their place till they 

 have excavated a hole sufficient to conceal themselves : but fu- 

 ture observation, by those who have the opportunity, will, there 



UO 10 ' .'.:7r-Gf 



with the opinions of that able observer. In Tab. VII. he has not only given beautiful 

 representations of the shell of the Photos dactylus, and its contained animal ; but has 

 displayed its anatomical structure in a series of figures which leaves nothing further 

 to be desired. M. POLI is clearly of opinion that the Pholades bore the rocks by me- 

 chanical action alone ; and he elsewhere adduces arguments to prove that even the 

 Mytilus lithophagits, the comparatively smooth shell of which seems unfitted for such 

 a purpose, forms its dwelling in a similar manner. The passage regarding the Pholas 

 is as follows : 



" Cryptas hujusmodi conicam formam pras se ferunt, angustiore sui parte sursum 

 versa, per quam Molluscum Pholadem incolens tracheas pro lubitu exerit. Earum 

 amplitude Pholadum aetati, atque magnitudini respondere videtur : in adultis duos 

 circiter pedes in altitudinem patet, et hiatus diameter quinque lineas minus excedit. 

 In junioribus, mollusca turn pede exerto, ac in terebrae formam accommodate, turn 

 etiam conchas ministerio circa pedis apicem veluti circa axem revolutas, cryptam pro- 

 fundiorem, latioremque efficiunt quemadmodum adolescunt. Tanta est motus hu- 

 jusmodi efficacia, ut lapidibus simul perterebrandis par est."" J. X. POLI, Testacea 

 utriusque Sictlite eorumque Historia et Anatome, vol. i. p. 40. Parma 1791. 



* " Ego crediderim in saxorum cavernulis vel vi vel natura factis, aquas marina: 

 appulsu procreari atque in concham verti, qua? cavitatis sive foraminis figuram servat -" 

 RONDELET. De Testaceis, lib. i. p. 49. Lugd. 1555. 



