VIEWS OF ERASMUS DARWIN 371 



be entirely new at the time of its production ; and therefore it 

 may retain some of the habits of the parent-system." 



Here we have clearly expressed the idea of continuity which 

 plays such an important part in modern theories of heredity. 

 Erasmus Darwin was, however, a " Spermatist," that is to say 

 he believed 



" that the embryon is produced solely by the male, and that the 

 female supplies it with a proper nidus, with sustenance, and 

 with oxygenation ; and that the idea of the semen of the male 

 constituting only a stimulus to the egg of the female, exciting it 

 into life, (as held by some philosophers) has no support from 

 experiment or analogy." 



It must be remembered that he wrote in the days before the 

 cell theory had shed its illuminating rays over the science of 

 embryology : 



"I conceive," says he, "the primordium, or rudiment of the 

 embryon, as secreted from the blood of the parent, to consist of a 

 simple filament as a muscular fibre," 



but this filament was not necessarily thread-like in form, for 

 he adds : 



" I suppose this living filament, of whatever form it may be, 

 whether sphere, cube, or cylinder, to be endued with the capability 

 of being excited into action by certain kinds of stimulus." 



It thus absorbs nutriment and becomes organized by "accre- 

 tion of parts," and this leads to the development of new kinds 

 of " irritability." According to this view the appearance of a 

 new organ precedes its use : 



" the lungs must be previously formed before their exertions to 

 obtain fresh air can exist." 



"From hence I conclude, that with the acquisition of new 

 parts, new sensations, and new desires, as well as new powers, are 

 produced ; and this by accretion to the old ones, and not by 

 distention of them." 



But the exercise of these new powers in turn gives rise to the 

 development of more new parts, which 



" are formed by the irritations and sensations, and consequent 

 exertions of the parts previously existing, and to which the new 

 parts are to be attached." 



" From this account of reproduction it appears, that all animals 

 have a similar origin, viz. from a single living filament ; and 



B 2 



