THE PRODROMUS 251 



softer, and both fibrous; a careful examination of these is as 

 illuminating as an investigation of bones. 



4. That all the subdivisions, if you exclude the outermost or 

 smallest, were produced between the outer shell and the body 

 of the animal itself, and so have received their forms, not from 

 themselves, but from their place; the result of this is that in 

 the case of oysters the motion of the animal, and the amount 

 of substance, often give rise to some diversity of form. With 

 regard to the outermost shell there can be a doubt whether the 

 surrounding fluid has touched the outer surface or whether it 

 has been protected by a membrane. I should, however, believe 

 that the last view alone is correct: (i) Because the filaments 

 of all the rest of the subdivisions were untouched by the sur- 

 P. 55. rounding fluid at the time when they formed. (2) Because in 

 prickly cockles we see that something like a membrane or skin 

 covers the outside of the shells. But the inquiry concerns 

 something almost outside the realm of vision, and it can be 

 said that the filaments of the first subdivision had already hard- 

 ened within the egg, since experimental knowledge proves that 

 oysters and other testacea spring from eggs, not from decaying 

 matter.^ 



From what has been said it is easy to explain : 

 I. All the diversity of hues and of spines which arouse the 

 wonderment of many in the case of shells not only from our 

 own land, but also from other lands ; for it has no other origin 

 than the edge of the animal enclosed in the shell. This edge, 

 gradually growing and expanding from something exceedingly 

 small, leaves its impress upon each margin of the subdivisions, 

 since these margins either form from the fluid which is exuded 

 from the outer edge of the animal, or are themselves the 

 creature's outer edges which, like the teeth of the shark, grow 



1 Theories of spontaneous generation were common among the Greek philosophers ; as, 

 e.g. Anaximander, in Gi&Xs, Fragmente der Vorsokratiker (Zweite Auflage, Berlin, 1906), p. 17, 

 and especially Aristotle, de Animaliuni Historia, V. i, 3, and de Generatione Animalium, I. 

 23 ; III. 9, 10, and 11. Steno's friends were the first to combat them scientifically ; so Harvey, 

 Exercitationes de Generatione Animaliujn (London, 1651) ; Francesco Redi, Esperienze 

 intorno alia Generazione degV Insetti (Florence, 1668) ; Swammerdam, Historia Inseciorum 

 Generalis (Utrecht, 1669). See also Huxley, Address before the British Association, 1870, 

 in Lay Sermons, Addresses, and Reviews (New York, 1877), pp. 345-378. 



