136 Darwin, and after Darwin. 
I have dealt thus at considerable length upon the 
processes whereby the originally unicellular ovum and 
spermatozoén become converted into the multicellular 
germ, because I do not know of any other exposition 
of the argument from Embryology where this, the first 
stage of the argument, has been adequately treated. 
Yet it is evident that the fact of all the processes 
above described being so similar in the case of sexual 
(or metazoal) reproduction among the innumerable or- 
ganisms where it occurs, constitutes in itself a strong 
argument in favour of evolution. For the mechanism 
of fertilization, and all the processes which even thus 
far we have seen to follow therefrom, are hereby 
shown to be not only highly complex, but likewise 
highly specialized. Therefore, the remarkable simi- 
larity which they present throughout the whole animal 
kingdom—not to speak of the vegetable—is expressive 
of organic continuity, rather than of absolute dis- 
continuity in every case, as the theory of special 
creation must necessarily suppose. And it is evident 
that this argument is strong in proportion to the 
uniformity, the specialization, and the complexity of 
the processes in question. 
Having occupied so much space with supplying what 
appear to me the deficiencies in previous expositions 
of the argument from Embryology, I can now afford 
to take only a very general view of the more important 
features of this argument as they are successively fur- 
nished by all the later stages of individual development. 
But this is of little consequence, seeing that from the 
point at which we have now arrived previous exposi- 
tions of the argument are both good and numerous. 
The following then is to be regarded as a mere sketch 
