First we have the analogy that is supposed to be afforded by what takes place in the development of a single cell into a man in the space of a few years, and an alleged correspondence of development by which a single cell, in the course of untold millions of years, has given origin to the human race. Granting any difference of time which this comparison calls for, and substituting in place of the successive moments or years of an individual life, from the formation of the ovum to the fully developed animal, the successive generations of any imaginable series of animals, the question is not merely what we can definitely conceive, or how successfully we can construct a theory. It is whether the supposed analogy will hold; whether we can find that in the two cases development takes place in the same way or in a way that is so nearly alike in the two cases as to warrant us in reasoning from the one to the other. In the case of the development of the single cell into the mature animal, although we can not, either before or after birth, detect the changes that are taking place from minute to minute, the infinitesimal accretions or losses, we know that there is a perpetual and unbroken connection of life maintained from the moment when the fœtus is formed to the moment when the mature animal stands before us. Break this connection anywhere in the process of development, and life is destroyed; the development is at once arrested. It is this connection that constitutes, as I presume, what the learned author calls the "appropriate conditions," in the case of the production of the individual animal; it is, at all events, the one grand and indispensable condition to the development of the cell into the fœtus, of the fœtus into the newly born child, and of the child into the man. Now, if we are to reason from this case of individual development to the other case of successive generations of creatures differing from each other in the same or any other ratio in which the perfect man differs from the ovum, the fœtus, or the newly born child, which are all successive stages of one and the same individual life, we ought to find in the successive generations of the different creatures some bond of connection, some continuity of lives with lives, some perpetuation from one organism to another, that will constitute the "appropriate conditions" for a corresponding development from a single cell through the successive types of animal life into the human race. Without such connection, continuity, perpetuation from organism to organism, shown by some satisfactory proof, we have nothing but a theory, and a theory that is destitute of the grand conditions that will alone support the analogy between the two cases. If anywhere in the supposed chain of successive generations of different animals the continuity of animal and animal is broken, the hypothesis of special creations of new organisms must come in: for we must remember that