xr PHENOMENA OF ORGANIC NATURE 327 



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 develop- 

 ment, he can do it. For we shall find that, dis- 

 tinct 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 a nitro- 

 genous 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 organi- 

 sation " of the animal kingdom which has been 

 guessed at and fancied for many years ; but which 

 it has been left to the present time to be demon- 

 strated by the careful study of development. 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 con- 

 dition of form ? Is there among the plants the 

 same primitive form of organisation, 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 nitrogenous 

 matter having substantially the same conditions. 

 So that if you trace back the oak to its first 



