116 HYPOTHESIS OF THE DEVELOPMENT OP 



This organ will, perhaps, be seen serving a purpose in a par- 

 ticular family of animals ; but we advance into an adjoining 

 or kindred family, and there find a rudiment of the same 

 organ, which, owing to the different conditions of this new 

 set of creatures, is of no kind of service. Thus, some of the 

 serpent tribes possess rudimentary limbs. In other instances, 

 a portion of organization necessary in one sex is also pre- 

 sented in the other, where it is not necessary. For example, 

 the mammae of the human female, by whom these organs are 

 obviously required, also exist in the male, who has no occasion 

 for them. It might be supposed that in this case there was a 

 regard to uniformity for mere appearance' sake ; but that no 

 such principle is concerned, appears from a much more re- 

 markable instance connected with the marsupial animals. 

 The female of that tribe has a process of bone advancing 

 from the pubes for the support of her pouch ; and this also 

 appears in the male marsupial, who has no pouch, and re- 

 quires none. 



The same law of unity presides over the vegetable king- 

 dom. Amongst phanerogamous plants, a certain number of 

 organs are always present, either in a developed or rudi- 

 mentary state ; and those which are rudimentary can be 

 developed by cultivation. The flowers which bear stamens 

 on one stalk and pistils on another, can be caused to produce 

 both, or to become perfect flowers, by having a sufficiency of 

 nourishment supplied to them. So, also, where a special 

 function is required for particular circumstances, nature 

 provides for it, not by a new organ, but by a modification of 

 a common one. Thus, for instance, some plants destined to 

 live in arid situations, require to have a store of water which 

 they may slowly absorb. The need is arranged for by a cup- 

 like expansion round the stalk, in which water remains after 

 a shower. Now the pitcher, as this is called, is not a new 

 organ, but simply the metamorphosis of a leaf. 



It is thus proved, with regard to the constituent beings of 

 large sections of the animal kingdom, that they are bound up 

 in a fundamental unity, however various in degree of endow- 



