730 3Ir. Edivard A. Minchin [May 6, 



whicli is not that which it would naturally assume. We can observe 

 that it does so, and that not only in this, but in many other cases, 

 living bodies appear to have the power of modifying and transforming 

 their component materials in a way which we are far from under- 

 standing. Ko sooner, however, is this mysterious change effected 

 than the crystal has crossed, so to speak, the line which separates the 

 living from the lifeless world, and must now be regarded from an 

 entirely different standpoint, that is to say, as a part of a living body. 

 As such it is subject to new influences and is governed by new laws, 

 which, as it were, override those by which the lifeless crystal is ruled. 

 In the first place, it must be supposed that each spicule, had it been 

 deposited in an inorganic matrix, would have had the characteristic 

 contours of an ordinary crystal of calcite. This receives, in fact, 

 further proof from the interesting observations of Sollas, who showed 

 that upon sponge spicules j^laced in a solution of carbonate of lime, 

 new layers of calcite are deposited, which tend to restore the ordinary 

 crystalline form. Instead of that, however, it has a form which can- 

 not be brought into any relation with its intrinsic crystalline prof»er- 

 ties. It is true that the attempt has been made to ex]3lain the 

 symmetry often exhibited by the spicules as due to their crystalline 

 nature. Not only, however, can any such explanation be shown to be 

 inadequate in itself, but it is also quite unnecessary, since in other 

 sponges, spicules even more symmetrical may occur, which are manu- 

 factured, so to speak, out of a non-crystalline material, namely, colloid 

 silica. The symmetry and regularity of form which sponge spicules 

 often possess are clearly, therefore, not due to the inherent properties 

 of the material of which they are composed, but to the action of the 

 living matrix in which they are deposited. The symmetry of a 

 crystal, on the other hand, is one wdiich in its fundamental traits is 

 entirely independent of the matrix in which it is dei)osited. We 

 have seen further that in a natural crystal the parts cannot vary 

 independently. But in the living crystals every part varies indepen- 

 dently of all the others, according to the needs of the organism, and 

 the spicules can be traced through a long series of evolutionary 

 changes, resulting in the many different forms with which we are 

 acquainted. 



We may therefore sum up with regard to these living crystals 

 as follows. Their constitution is that of the calcite crystal, but 

 their external form is that which the sponge requires, and not that 

 which they would naturally assume. They furnish us, in fact, with 

 a beautiful instance of what is termed adaptation, that is to say, the 

 fact that any living organism tends to have just that form, structure 

 and organisation in all its parts which it requires in order to main- 

 tain its existence in its peculiar mode of life, whatever it may be. 



The principle of adaptation raises many scientific and philosophical 

 questions of great importance, but certain points may be emphasised 

 which have been seen in the instances under discussion. In the first 



