2s6 NICOLAUS STENO 



like those which ^ a certain kind of mussel inhabits in the 

 rocks of Ancona, Naples, and Sicily. These cavities in the 

 p. 60. rocks, unless they were formed by insects building a nest out of 

 mud (a thing which I can scarcely believe, since the substance 

 of the middle of the rock, where no cavities are found, is identi- 

 cal with the substance of the rock containing the cavities, which 

 are all confined to the surfaces), must have been eaten out by 

 worms ; and this view is not only commended by the surface of 

 the cavity, but also proved by a body composed of rather thick 

 filaments which is found in many cavities, and which answers 

 to the cavity itself in size and shape. Surely, the cavities were 

 made neither by mussels nor around mussels, since testacea of 

 this kind lack the organs for gnawing, and no cavity corre- 

 sponds to the shape of the shells.^ Nor is it surprising that 

 rocks exposed to the sea afford a resting place, in their cavities, 

 for mussels' eggs which have been cast up by the sea, for I have 

 not yet seen any of those cavities lacking an evident exit. But 

 if one say that the cavities were made by a petrifying fluid 

 which became hard around certain bodies, some cavities would 

 have been found enveloped by that same substance on every 

 side, and lacking an exit. 



4. A shell partly destroyed on the inside, where a marble in- 

 crustation covered by various balanoids had supplied the loss 

 of the substance eaten away ; so that it is possible to infer with 

 certainty that the shell had been left upon land by the sea, next 

 carried down into the sea ; again covered by a new deposit, and 

 abandoned by the sea. 



5. Very small eggs and helical shells hardly visible except 

 with the aid of the microscope. 



P. 61. 6. Pectens, helical shells, and bivalve mollusks not covered 

 with crystal but crystalline in all their substance. 

 7. Various tubes of sea worms. 



' The Florentine edition lias quos : read quas. 



The cavities, containing the thick filaments referred to by Steno, were probably made by 

 the Lithophagus (Lithodomus). This Lamellibranch, of the family Mytilidae, perforates shells 

 of the Lamellibranchs Melina, Ostrea, and Pectin, and produces a flask-shaped excavation. 

 See von Zittel, Grundziige der Palaontologie, Dritte Auflage, i Abteilung (MUnchen, 1910), p. 

 322 and fig. 632 c. 



^ The borer is a mussel ; cf. the preceding note. 



