90 'DETERMINANTS' VERSUS 



Planariae and other worms (though not among Free Nematoids) ; 

 till, when we come to Crustacea, Insects, and Amphibia the power 

 of reproduction after injury dwindles down, and is confined in the 

 main to a power of regenerating lost limbs or appendages, and in 

 Mammalia to a power of repairing wounds. 



In some of these lower organisms the power of repair is just as 

 great as it is among some plants, as Weismann himself fully admits. 

 Thus concerning one of the common Polyps he says : — " Not only 

 has Hydra been cut in from two to twenty different pieces, but 

 it has even been chopped up into innumerable fragments, and 

 yet each of these, under favourable circumstances, was able to 

 grow again into a complete animal." Then, concerning certain 

 common worms, Planariae, he says : — " Through the experiments 

 of Loeb, Morgan, Voigt, Bickford, and others, we know that these 

 animals respond to almost every mutilation by complete recon- 

 struction, that they may, for instance, as is indicated in Fig. 96, be 

 cut transversely into nine or ten pieces, with the result that each of 

 these pieces grows again to a whole animal, unless external 

 influences are unfavourable and prevent it." While in regard 

 to another little worm found in ponds, Lumbriculus, he adds, 

 " Certainly the power of regeneration is so great in this animal that 

 it is out of the question to talk of localising the primary constituents 

 of regeneration ; almost every broken surface is capable of 

 regeneration." 



In his two lectures on " Regeneration " Weismann makes an 

 ingenious but laboured attempt to bring all this class of facts into 

 harmony with his views as to the ' Continuity of the Germ Plasm,' 

 and the all-powerful influence, even in lowest organisms, of 

 ' natural selection.' Thus he says : — " My own view is that the 

 regenerative capacity is not something primary, but rather an 

 adaptation to the organism's susceptibility to injury, that is, a 

 power which occurs in organisms in varying degrees, proportionate 

 to the degree and frequency of their liability to injury. Regenera- 

 tion prevents the injured animal from perishing, or from living on 

 in a mutilated state, and in this lies an advantage for the main- 

 tenance of the species." But even in accordance with this view 

 that the regenerative capacity is a secondary and acquired, rather 

 than a primary, property of the living matter of the organisms 

 possessing it, he is obliged to postulate the existence in all kinds of 

 cells, in the animals in question, of " inactive accessory idioplasm," 

 — that is, of hosts of his determinants, usually latent, but capable of 



