We may therefore describe the aforesaid principle as a maxim for judging of the internal purposiveness of organised beings.

It is an acknowledged fact that the dissectors of plants and animals, in order to investigate their structure and to find out the reasons, why and for what end such parts, such a disposition and combination of parts, and just such an internal form have been given them, assume as indisputably necessary the maxim that nothing in such a creature is vain; just as they lay down as the fundamental proposition of the universal science of nature, that nothing happens by chance. In fact, they can as little free themselves from this teleological proposition as from the universal physical proposition; for as without the latter we should have no experience at all, so without the former