380 PEOVISIOXAL HYPOTHESIS Cm .p. XXVII. 



Hardly any fact in plij'siology is more wonderful than the 

 power of re-growth ; for instance, that a snail should be able 

 to reproduce its head, or a salamander its eyes, tail, and legs, 

 exactly at the points where they haA^e been cut off. Such 

 cases are explained by the presence of gemmules derived from 

 each part, and disseminated throughout the body. I have 

 heard the process compared with that of the repair of the 

 broken angles of a crystal by re-crystallisation ; and the two 

 processes have this much in common, that in the one case 

 the polarit}" of the molecules is the efficient cause, and in the 

 ©ther the affinity of the gemmules for particular nascent cells. 

 But we have here to encounter two objections which apply 

 not only to the re-growth of a part, or of a bisected individual, 

 but to fissiparous generation and budding. The first objection 

 is that the part which is reproduced is in the same stage of 

 development as that of the being which has been operated on 

 or bisected; and in the case of buds, that the new beings thus 

 produced are in the same stage as that of the budding parent. 

 1'hus a mature salamander, of which the tail has been cut 

 off, does not reproduce a larval tail ; and a crab does not 

 reproduce a larval leg. In the case of budding it was 

 shown in the first part of this chapter that the new being 

 thus produced does not retrograde in development, — that 

 is, does not pass through those earlier stages, which the 

 fertilised germ has to pass through. Kevertheless, the organ- 

 isms operated on or multipl3dng themselves by buds must, 

 by our hypothesis, include innumerable gemmules derived 

 from every part or unit of the earlier stages of development ; 

 and why do not such gemmules reproduce the amputated 

 part or the whole body at a corresponding early stage of 

 development ? 



The second objection, which has been insisted on by Delpino, 

 is that the tissues, for instance, of a mature salamander or crab, 

 of which a limb has been removed, are already differentiated 

 and have passed through their whole course of development ; 

 and how can such tissues in accordance with our hypothesis 

 attract and combine with the gemmules of the part which is 

 to be reproduced ? In answer to these two objections we must 

 bear in mind the evidence which has been advanced, showing 



