326 THE EVOLUTION THEORY 



modified form, by many esteemed naturalists, and so it does not seem 

 superfluous to discuss it in more detail. 



I have already noted that we see in conjugation an amphimixis 

 without reproduction, and in spores and parthenogenetic ova repro- 

 duction without amphimixis, and I do not doubt that every 

 unprejudiced critic will admit this ; many among us, however, are 

 not unprejudiced, but are under the spell of earlier ideas, so that they 

 cannot forget that it was long believed that fertilization was an 

 indispensable condition of development; they therefore regard the 

 divisions which recommence sooner or later after conjugation, and 

 which may be repeated hundreds of times, as conditioned by the 

 conjugation which 'preceded them, and compare them to the series of 

 cells which, in the Metazoa, lead from the fertilized ovum to the fully- 

 formed animal. They regard both series of cell-generations as a 

 developmental cycle, which leads from fertilization to fertilization 

 again, from conjugation to conjugation, and which would be impossible 

 without either fertilization or conjugation. 



This play with the idea of a ' cycle ' reminds me vividly of 

 similar fantastic play from the time of the much-despised ' Natur- 

 philosophie' of a hundred years ago. As men sought to find the 

 analogues of ' solar ' and ' planetary ' systems in animal and plant, and 

 believed they had stated something when they compared the motile 

 animals to planets and the sedentary plants to the sun (!), so it is now 

 imagined that a deeper insight has been gained by the recognition of 

 cycles of development. By all means let us regard the development 

 of a multicellular organism as cyclic ; it returns again to its starting- 

 point, but this no more explains the forces which produce the cycle, 

 and thus the meaning of fertilization, than a comparison with the 

 circling planets explains the causes of locomotion in animals. With 

 quite as much reason the cycle of development might be made to start 

 from the parthenogenetic ovum, and then the whole conclusion of the 

 fanciful cycle idea in regard to the meaning of fertilization falls to 

 the ground, for in this case the cycle begins without fertilization. 

 Attempts are made to get over this difficulty by showing that in many 

 cases parthenogenesis alternates regularly or irregularly with sexual 

 reproduction, as in the water-fleas (Daphnids), the Aphides, and so on. 

 The mysterious rejuvenating power of amphimixis is supposed to 

 suffice for several generations, a purely gratuitous assumption, which 

 is also in open contradiction to the facts. For there are species which 

 now reproduce exclusively by parthenogenesis, among plants for 

 instance, a number of fungi, among animals a few species of 

 Crustaceans. Of the latter it can be demonstrated that ages ago they 



