OF ORGANIC NATURE 25 



But can we go no further than that ? When one has 

 got so far, one is tempted to go on a step and inquire 

 whether we cannot go back yet further and bring down 

 the whole to modifications of one primordial unit. The 

 anatomist cannot do this ; but if he call to his aid the 

 study of development, he can do it. For we shall find 

 that, distinct as those plans are, whether it be a porpoise 

 or man, or lobster, or any of those other kinds I have 

 mentioned, every one begins its existence with one and the 

 same primitive form, that of the egg, consisting, as we 

 have seen, of an introgenous substance, having a small 

 particle or nucleus in the centre of it. Furthermore, the 

 earlier changes of each are substantially the same. And 

 it is in this that lies that true " unity of organization " of 

 the animal kingdom which has been guessed at and fancied 

 for many years ; but which it has been left to the present 

 tune to be demonstrated by the careful study of develop- 

 ment. But is it possible to go another step further still, 

 and to show that in the same way the whole of the organic 

 world is reducible to one primitive condition of form ? Is 

 there among the plants the same primitive form of organiza- 

 tion, and is that identical with that of the animal kingdom ? 

 The reply to that question, too, is not uncertain or doubtful. 

 It is now proved that every plant begins its existence under 

 the same form ; that is to say, in that of a cell a particle 

 of introgenous matter having substantially the same ft 

 conditions. So that if you trace back the oak to its first / 

 germ, or a man, or a horse, or lobster, or oyster, or any / 

 other animal you choose to name, you shall find each and 

 all of these commencing their existence in forms essentially 

 similar to each other : and, furthermore, that the first I 

 processes of growth, and many of the subsequent modifica-l 

 tions, are essentially the same in principle in almost all. ~t 



In conclusion, let me, in a few words, recapitulate the 

 positions which I have laid down. And you must under- 

 stand that I have not been talking mere theory ; I have 

 been speaking of matters which are as plainly demonstrable 

 as the commonest propositions of Euclid of facts that 

 must form the basis of all speculations and beliefs in 

 Biological science. We have gradually traced down all 

 organic forms, or, in other words, we have analyzed the 

 present condition of animated nature, until we found that 

 each species took its origin in a form similar to that under 

 which all the others commence their existence. We have 



