date to convince us of our mistake. If we observe that the forms of the parts of animals are always perfect when viewed in relation to their use, as is really the case, it is not to be inferred that it is the form of the parts which has led them to be employed in a certain way, as zoologists assert, but that it is, on the contrary, the need of action which has produced the peculiar parts, and it is the employment of these parts which has developed them, and established a proper relation between them and their functions. To affirm that the form of the parts induced their functions, would be to leave Nature without power, incapable of producing any act, or any change in bodies; and the different parts of animals, as well as the animals themselves, as all created at first, would from that moment present as many forms as are required by the diversity of circumstances in which animals live; and it would be necessary that these circumstances should never vary, and that such should likewise be the case with the parts of each animal. Nothing, however, of this kind takes place, and nothing can be more opposite to the means which observation shows us that Nature employs to call into existence her manifold productions. It must hence appear, that what are called species do not exist in nature; that the constancy of races to which that name has been given, can only be temporary and not absolute, although they would no doubt continue the same as long as the circumstances which effect them undergo no change, and they are not forced to alter their ha-
