(.I:MI;\I. DISCUSSIn\ Of rm: H - OP DEVI 83 



offunfa f abor 



<ln> ///.s7A /'''"'' i/(rft'f'ittitifion associuf"/ n-itfi it. In order to 

 understand fully tin' significant' of tliis principle in di -velopment, 

 we must proceed from tin- th'>i- that tin- life of all organic 1 

 expresses it>-lf in a - \- :<>us dutis or functions. Organisms 



t ike to t h- in-- Ivi s substances from wit hout : t hey incorporate in t h< ir 

 loili.sthat which is serviceable, ami liminate (hat which is not 

 (function of nutrition and metastasis); they can alt.-r the form of 

 iln ir bodies by mntrai'tion and extension (function of motion) ; tln-y 

 an- capable of reacting upon external stimuli (function of SCUM! ility i : 

 thty possess the ability to bring forth n.-\v organisms of tin ii 

 kind (function of reproduction). Intbelowtst mult ic-llidar organisms 

 t ach of the individual parts discharges in the same manner as the 

 others tin- t mini' rai d functions necessary for organic life; bu- 

 nion highly nu organism is developed, the more do we see that it- 

 individual ci-lls ditl'nvntiatt' themselves for the duties of life, that 

 some assume the function of nutrition, others that of motion, others 

 th:.t of s- nsibility, and still others that of reproduction, and that with 

 this division of labor is likewise joined a greater degree of com- 

 plrtuiiss in the execution of the individual functions. The 

 development of a specialised duty likewise leads invariably \. 



altind apjM'aiancc of tin- rt-11 : ////// tin }> // Division of 



- ijves loii /iiorpholo'jifil or fa 



Klem tut a rv j a i'ts which a i-i especially concerned in the duties of 

 nutrition are distinguished as gland-cells ; again others, \\hich have 

 <!e\. loped the power of contractility to a greater extent, have 

 become muscle-ct 11s. othi rs m-rvc-c-i-lls, others sexual ci-ll>. etc. The 

 which are c< nceincd in one and the same duty are for the most 

 pait assoriattd in LTTOUPS, and const it ut e a >p: cial ti->u-. 



'Thus the >tmly of tin' finbi-ytiloMy of an organi-m emhrao > chi- tly 

 two eleini r.t- : die i> the study of the dev lojM rm, the 



> coml the study of hi>tological differentiation, \\"e may at the 

 >ame time add that in the case of the higher organisms the moi 

 logii- il chang. s are accomplish* d principally in the arlier stages of 

 devrlopnn nt, ami that th.- Ideological differentiat ion takes place in 

 the final 



A kiu'wltdge of these leading principles will materially facilitate 

 the Comprehension of the further pr< 



