IX] AND SPICULAR SKELETONS 415 



or its shell. Thus, Pouchet and Chabry* have shown that the 

 eggs of sea-urchins reared in lime-free water develop in apparent 

 health, into larvae entirely destitute of the usual skeleton of 

 calcareous rods, and in which, accordingly, the long arms of the 

 Pluteus larva, which the rods support and distend, are entirely 

 suppressed. And again, when Foraminifera are kept for genera- 

 tions in water from which they gradually exhaust the lime, their 

 shells grow hyaline and transparent, and seem to consist only of 

 chitinous material. On the other hand, in the presence of excess 

 of hme, the shells become much altered, strengthened with various 

 "ornaments," and assuming characters described as proper to 

 other varieties and even species f. 



The crucial experiment, then, is to attempt the formation of 

 similar structures or forms, apart from the living organism : but, 

 however feasible the attempt may be in theory, we shall be prepared 

 from the first to encounter difficulties, and to realise that, though 

 the actions involved may be wholly within the range of chemistry 

 and physics, yet the actual conditions of the case may be so 

 complex, subtle and delicate, that only now and then, and in the 

 simplest of cases, shall Ave find ourselves in a position to imitate 

 them completely and successfully. Such an investigation is only 

 part of that much wider field of enquiry through which Stephane 

 Leduc and many other workers J have sought to produce, by 

 synthetic means, forms similar to those of living things ; but it 

 is a well-defined and circumscribed part of that wider investigation. 

 When by chemical or physical experiment we obtain configurations 

 similar, for instance, to the phenomena of nuclear division, or 

 conformations similar to a pattern of hexagonal cells, or a group 

 of vesicles which resemble some particular tissue or cell-aggregate, 

 we indeed prove what it is the main object of this book to illustrate, 

 namely, that the physical forces are capable of producing particular 

 organic forms. But it is by no means always that we can feel 

 perfectly assured that the physical forces which we deal with in 

 our experiment are identical with, and not merely analogous to, 



* C. R. Soc. Biol. Paris (9), i, pp. 17-20, 1889; C. i?. Ac. 8c. cvm, pp. 196-8, 



1889. 



t Cf. Heron-Allen, Phil. Trans. (B), vol. ccvi, p. 262, 1915 



J Sec Leduc, Mechanism of Life (1911), oh. x, for copious references to other 



works on the artificial production of "organic" forms. 



