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 Spongiadz to the 
Vertebrata as a primordial common property, 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.” 
