THE BEGINNING OF LIFE. 221 



must be extremely important, but it is for the palpable 

 reason that the theory thereby gains the support and 

 corroboration of another great series of facts. 



If the accordance of the evolution of families has 

 once been followed up to the Gastrula, we shall not 

 pause there, but must regard the similarity of the sperm 

 corpuscules and germ cells from the Spongiadae to the 

 Vertebrata as a primordial common propert}^, con- 

 necting the animal and vegetal world ; and prior to the 

 acquisition of which, only those modes of reproduction 

 took place which have been maintained among Protista 

 and in heterogenesis. 



As the common basis of sexual reproduction in the 

 various families argues a common origin, asexual re- 

 production, directly connected as we have seen it to 

 be with sexual propagation, by means of unfecundated 

 eggs and germs, leads us constantly further towards the 

 beginning of life. But the cell furnished with a nucleus 

 and sheath is inseparable from the protoplasmic cor- 

 puscule devoid of nucleus or sheath, on the growth and 

 fission of which rests the reproduction of the lowest 

 living beings. 



Their origin from inorganic matter, as we have set 

 forth above, is a postulate of sound human under- 

 standing. To this beginning we are led, not, as the 

 opponents of the doctrine of Descent are wont to say, 

 by a dogmatic after-philosophy, but by the unpre- 

 judiced consideration and computation of the facts of 

 individual development.*^* 



