FUNCTION. 159 



heart generate aiternating currents in the crude and dilute 

 nutriment occupying the peri-visceral cavity. How the func- 

 tion of transferring force, thus vaguely indicated in these in- 

 ferior forms, comes afterwards to be the definitely-separated 

 office of a complicated apparatus made up of many parts, each 

 of which has a particular portion of the general duty, need 

 not be described. It is sufficiently manifest that this o-eneral 

 function becomes more clearly marked-oflf from the others, 

 at the same time that it becomes itself oarted into subordinate 

 lunctionb 



In a developmg emorvo, tne functions or more strictly 

 the structures whicn are to perform tnem, arise in the same 

 general order. A like primarv distinction very early ap- 

 pears between the endoderm and the ectoderm — the part 

 which has the office of accumulating force, and the part out 

 j{ which grow those organs that are the great expenders of 

 force Between these two there presently becomes visible 

 the rudiment of that vascular system, which has to fulfil the 

 intermediate duty of transferring force. Of these three 

 general functions, that of accumulating force is carried on 

 from the outset * the endoderm, even while yet incompletely 

 differentiated from the ectoderm, absorbs nutritive matters 

 from the subjacent yelk The trpjisfer of force is also to 

 some extent effected by the rudimentary vascular system, as 

 Boon as its central cavity and attached vessels are sketched 

 out But the expenditure of force (in the higher animals at 

 least) is not appreciably displayed by the ectodermic struc- 

 tures that are afterwards to be mainly devoted to it : there 

 18 no sphere for the actions of these parts. Similarly 



with the chief subdivisions of these fundamental functions. 

 If we look at those discharged by the ectoderm, potentially 

 if not actually, we see that the distinction first established 

 separates the office of transforming other force into mechani 

 cal motion, from the office of liberating the force to be so 

 transformed — in the midst of the part out of which the mus- 

 cular svstem is to be developed, there is marked-out the 



