100 Mr Carpenter 07i Unity of Function 



gous to the nutritive system in the Vertebrata, or from looking 

 in the MoUusca for any representation of their locomotive ap- 

 paratus. Moreover, it usually happens that the development 

 of the different systems does by no means proceed pari passu, 

 and hence the embryo cannot be considered as presenting in 

 its totality any resemblance or analogy with beings beneath it : 

 and it is deficient in this very important faculty, the power of 

 maintaining its own existence. But in certain cases where it is 

 necessary that it should possess this power, it is attained by 

 preserving such a harmony in the development of the different 

 systems, that they shall all act in unison with one another ; and 

 the being does then present a perfect transitory resemblance to 

 those of the class beneath. Thus it would be difficult to de- 

 monstrate that the tadpole is not a fish pro tempore ; no natu- 

 ralist would hesitate in what class to place it, if only acquainted 

 with its early form ; and the same observation will apply to the 

 caterpillar, whose structure is altogether that of the annelides. 

 Taking this view of the case, therefore, metamorphosis does 

 not essentially differ in nature from those changes which every 

 animal undergoes in the progress of its development ; but the 

 embryo is adapted for deriving its subsistence from the world 

 around, instead of from its parent, by causing the development 

 of all its structure to go on pari passu, so that each organ may 

 hai-monize in function with the rest. 



Putting aside, however, for the present tliese extraneous but 

 deeply interesting questions, I proceed to the proper subject of 

 this paper, which is, to apply to Jtinciion one of the laws pro- 

 pounded by Von Bar with regard to structure, namely, that, 



1. A special function arises only out of one more general, 

 and this by a gradual change. 



To this law I shall add a second, that, 



2. In all eases where the different functions are highly spe- 

 cialized, the general structure retains, more or less, the primi- 

 tive community of function which originally characterized it. 



The division of the changes which take place during the ex- 

 istence of the living animal body into the orsyanic functions, 

 and those exclusively animal, will answer very well for my 

 present purpose, although, as we shall presently observe, it is 

 only in the more specialized forms that we see them distinctly 



