THE BEGINNINGS OF II FE. 1 25 



dually increase, and different ^ organs^ slowly appear, 

 varying in structure and arrangement in accordance 

 with the nature of the organism whose evolution is 

 being watched; so that, as Von Baer^ originally pointed 

 out, a progress from the more general to the more 

 special is always to be observed during the development 

 of animals and plants. 



It is, therefore, only natural to suppose that homo- 

 geneous specks of living matter as they increase in 

 size should undergo certain diff^erentiating changes 

 whereby ^ structure ' is gradually evolved and more and 

 more complex functions are generated 2. We should, 

 however, have been utterly unable to predict the pro- 

 bable nature of such changes if we knew nothing of 

 present lower organisms, and of the microscopic ana- 

 tomy of the tissues of higher animals and plants during 

 the different phases of their development. But our 

 familiarity with these subjects has instructed us as to 



^ In his celebrated work entitled ' Ueber Entwickelungs-Geschichte,' 

 1828. The application of this law was subsequently developed by Dr. 

 Martin Barry, in the ' Edin. Philos. Journal' for 1837, and also quite 

 independently by M. Milne- Edwards in ' Ann. des Sc. Nat,' Ser. iii. t. i. 



* Mr. Spencer says (loc. cit., p. 387) : — ' In Organisms the advance 

 towards a more integrated, heterogeneous, and definite distribution of 

 the retained motion, which accompanies the advance towards a more 

 integrated, heterogeneous, and definite distribution of the component 

 matter, is mainly what we understand as the development of functions. 

 All active functions are either sensible movements, as those produced 

 by contractile organs; or such insensible movements as those propa- 

 gated through the nerves; or such insensible movements as those by 

 which, in secreting organs, molecular rearrangements are effected, and 

 new combinations of matter produced.' 



