318 THE INDUCTIONS OF BIOLOGY. 



assignable causes, are classed as " spontaneous/' For if the 

 assumption of a special arrangement of parts by an organism, 

 is due to the proclivity of its physiological units towards that 

 arrangement; then the assumption of an arrangement of 

 parts slightly different from that of the species, implies 

 physiological units slightly unlike those of the species; and 

 these slightly-unlike physiological units, communicated 

 through the medium of sperm-cell or germ-cell, will tend, in 

 the offspring, to build themselves into a structure similarly 

 diverging from the average of the species. 



But it is not equally manifest that, on this hypothesis, 

 alterations of structure caused by alterations of function 

 must be transmitted to offspring. It is not obvious that 

 change in the form of a part, caused by changed action, in- 

 volves such change in the physiological units throughout the 

 organism that these, when groups of them are thrown off in 

 the shape of reproductive centres, will unfold into organisms 

 that have this part similarly changed in form. Indeed, when 

 treating of Adaptation (§ 69), we saw that an organ modified 

 by increase or decrease of function, can but slowly re-act on 

 the system at large, so as to bring about those correlative 

 changes required to produce a new equilibrium ; and yet only 

 when such new equilibrium has been established, can we ex- 

 pect it to be fully expressed in the modified physiological units 

 of which the organism is built — only then can we count 

 on a complete transfer of the modification to descendants. 

 Nevertheless, that changes of structure caused by changes 

 of action must also be transmitted, however obscurely, ap- 

 pears to be a deduction from first principles — or if not a 

 specific deduction, still, a general implication. For if an 

 org-aiiiOTn A, has, by any peculiar habit or condition of life, 

 been modified into the form A', it follows that all the func- 

 tions of A', reproductive function included, must be in some 

 degree different from the functions of A. An organism 

 being a combination of rhythmically-acting parts in moving 

 equilibrium, the action and structure of any one part cannot 



