400 Weisnianns Theories — 



thesis he draws between the immortaUty of the Protozoa 

 and the mortahty of the Metazoa breaks down also. 



As to this matter, Dr. DalKnger has further observed 

 that after a prolonged continuity of fission (measured by 

 following persistently one-half of the fission in every case 

 to the end), there comes a period of death — absolute de- 

 vitalisation — to a majority of the individuals, after from 

 six to ten hours, according to the species ; while those 

 which do not thus die fuse together, and end by pro- 

 ducing a multitude of minute spores. 



This perfectly agrees with what M. E. Maupas has also 

 quite recently observed in Infusoria} After two hundred 

 and fifteen generations had been produced by ordinary 

 division, they either died a natural death, or blended with 

 individuals derived from another source, and so ceased 

 individually to exist. 



One of the most curious of the Professor's hypotheses is 

 that which denies all difference of sex, that is, of course, all 

 essential difference. This denial is indeed but one aspect 

 of his far wider denial of all differences of a qualitative kind 

 (p. 101), to the consideration of which we shall return later. 

 It is a fortunate denial, since certain consequences of the 

 position he has assumed can be tested by observation, and 

 have been so tested quite recently. 



If, as the Professor affirms, there is no difference of quality 

 between the sexes, then the fertilisation of flowers or insects 

 can but consist in a modification of its quantity. But among 

 lowly animals, certain so-called Avater-fleas, a few moths, 

 wheel-animalcules, and the green aphides which so affect 

 pelargoniums kept in dwelling-rooms, reproduce partheno- 

 genetically. It follows, therefore, if Professor Weismann is 

 right, that there must be a special quantitative difference 

 between the ova of such creatures and the ova of allied 



1 Archives de Zoologie Experimentale, 1888. 



