306 THE INDUCTIONS OF BIOLOGT. 



attributes whicli are common to tlie members of auy group 

 of the first, second, third, or fourth rank, we see that groups 

 of the widest generality are based on characteristics of the 

 greatest importance, physiologically considered ; and that the 

 characteristics of the successively-subordinate groups, are 

 characteristics of successively-subordinate importance. The 

 structural peculiarity in which all m^embers of one sub- 

 kingdom diifer from all members of another sub-kingdom, is 

 a peculiarity that affects the vital actions more profoundly, 

 than does the structural peculiarity which distinguishes all 

 members of one class from all members of another class. 

 Let us look at a few cases. 



We saw ( § 56), that the broadest division among the 

 functions is the division into " the accumulation of force 

 (latent in food) ; the expenditure of force (latent in the 

 tissues and certain matters absorbed by them) ; and the 

 transfer of force (latent in the prepared nutriment or blood) 

 from the parts which accumulate to the parts which expend." 

 Now the lowest animals, united under the general name 

 Protozoa, are those in which there is either no separation of 

 the parts performing these functions or very indistinct separ- 

 ation : in the Rhizopoda, all parts are alike accumulators of 

 force, expenders of force, and transferrers of force; and 

 though in the most differentiated members of the group, the 

 Infusoria, there are something like specializations corre- 

 sponding to these functions, yet there are no distinct tissues 

 appropriated to them. The animals known as Cwknterata 

 are characterized in common by the possession of a part 

 which accumulates force more or less marked off from the 

 part which does not accumulate force, but only expends it ; 

 and the Hydroeoa and Aciinozoa, which are sub-divisions of 

 the Caknterata, are contrasted in this, that in the one these 

 parts are very indefinitely distinguished, but in the other 

 definitely separated, as well as more complicated. Besides a 

 completer differentiation of the organs respectively devoted 

 to the accumulation of force and the expenditure of force, 



