204 AMPHIMIXIS OR ESSENTIA I MEANING OF [XII. 



one attains its object ; and these vast numbers are necessary 

 just because the way to the ^gg is so very precarious. Must 

 we regard this destruction as normal because it is so common ? 

 Is not fertihzation the normal aim of the vital processes of the 

 spermatozoon ? And does not the destruction of those numerous 

 spermatozoa which have missed their aim result from the fact 

 that they are not adapted for a long independent life, — that 

 their vital force is soon expended because no precaution has 

 been taken to renew it by food ? But has this lack of food been 

 brought about because it could not have been taken however 

 desirable it may have been ? I believe that spermatozoa want 

 a mouth, and all other adaptations for the absorption of nutri- 

 ment, because they do not need them for the attainment of the 

 object for which they exist, and that, were it otherwise, they 

 would have been adapted for living longer. Useless adaptations 

 are never met with. Spermatozoa gone astray are of no 

 further value to the species, and they may just as well disappear. 

 And so it is with those Infusoria which have failed to conjugate ; 

 they are useless to the species, since its maintenance requires 

 the periodical crossing of individuals and of this they are no 

 longer capable. If Infusoria were not adapted for this crossing 

 they could live on for ever without amphimixis, just as a par- 

 thenogenetic ^gg and its products live on without it. But those 

 very changes which make an Infusorian capable of conjugation 

 remove all possibility of unending life without it, just as the two 

 'reducing divisions' withdraw this possibility from the egg. 

 An even closer parallel can be drawn, for Kupffer and Bohm ' 

 have shown, by the case of Petromyzon, that there are animal 

 eggs which only undergo the first polar division before they 

 come in contact with the spermatozoon, the second following 

 after it has penetrated. Such eggs when unfertilized, contain 

 the quantity of germ-plasm required for embryogeny, but are, 

 nevertheless, incapable of parthenogenetic development. We 

 cannot at present recognize those intimate changes upon which 

 this incapabilit}^ must depend, but we may conclude that it 

 is a consequence of changes preparatory to amphimixis. The 

 eggs are so completely adapted for this event that their power 



^ Bohm ' Ueber die Befruchtung des Neunaugen-Eies.' Sitzgsber. d. 

 math.-phys. Klasse d. ba^^r. Akad. d. Wissensch., Munich, 1887. 



