SUFFICIENCY OF EVIDENCE. 351 
is a scientific “hypothesis,” but that it still requires to be 
“proved.” When these remarks are made by persons who 
do not possess the requisite empirico-philosophical culture, 
nor the necessary knowledge in comparative anatomy, em- 
bryology, and palzontology, we cannot be much offended, 
and we refer them to the study of those sciences. But 
when similar remarks are made by acknowledged special- 
ists, by teachers of zoology and botany, who certainly ought 
to possess a general insight into the whole domain of their 
science, or who are actually familiar with the facts of those 
scientific domains, then we are really at a loss what to 
say. Those who are not satisfied with the treasures of our 
present empirical knowledge of nature as a basis on which 
to establish the Theory of Descent, will not be convinced 
by any other facts which may hereafter be discovered; 
for we can conceive no circumstances which would furnish 
stronger or a more complete testimony to the truth of the 
doctrine of filiation than is even now seen, for example, in 
the well-known facts of comparative anatomy and ontogeny. 
I must here again direct attention to the fact, that all the 
great and general laws, and all the comprehensive series 
of phenomena of the most different domains of biology can 
only be explained and understood by the Theory of Develop- 
ment (and especially by its biological part, the Theory of 
Descent), and that without it they remain completely inex- 
plicable and incomprehensible. The internal causal con- 
nection between them all proves the Theory of Descent to 
be the greatest inductive law of Biology. 
Before concluding, I will once more name all those series 
of inductions, all those general laws of Biology, upon which 
this comprehensive law of development is firmly based. 
