890 



SCIENCE. 



[N. S. Vol. XI. No. 284. 



stimulus. It is difficult for us to understand 

 instincts, because with us almost all devel- 

 opmental processes are extremely slow and 

 gradual. This particularly applies to the 

 development of those nervous mechanisms, 

 the working of which we call reason. 



Within certain limits the external condi- 

 tions may vary without harming the organ- 

 ism, but such variations are generally ac- 

 companied by variations in the form in which 

 the properties of the zygote are displayed. 

 If the variations of the conditions are too 

 great, their action upon the organism is in- 

 jurious, and results in abortions or death. 

 And in no case can the external conditions 

 call out properties with which the zygote 

 was not endowed at the act of conjugation. 



It would thus appear that acquired char- 

 acters are merely phases of development ; 

 they are the manifestations of the proper- 

 ties of the zygote, and are called forth only 

 under appropriate stimulation ; moreover, 

 they are capable of varying within certain 

 limits, according to the nature of the stim- 

 ulus, and it is to these variations that the 

 term acquired character has been ordinarily 

 applied. 



A genetic character, on the other hand, 

 is the possibility of acquiring a certain 

 feature under the influence of a certain 

 stimulus ; it is not the feature itself — that 

 is an acquired character — but it is the pos- 

 sibility of producing the feature. Now as 

 the possibility of producing the feature can 

 only be proved to exist by actually produc- 

 ing it, the term genetic character is fre- 

 quently applied to the feature itself, which 

 is, as we have seen, an acquired character. 

 In consequence of this fact, that we can 

 only determine genetic characters by exam- 

 ining acquired characters, a certain amount 

 of confusion may easily arise, and has in- 

 deed often arisen, in dealing with this sub- 

 ject. This can be avoided by remembering 

 that in describing genetic characters account 

 must always be taken of the conditions. 



For example, the white fur of the Arctic 

 hare is an acquired character, acquired in 

 response to a certain stimulus ; while the 

 power of so responding to the particular 

 stimulus when applied at the correct time 

 is a genetic character. Thus a genetic 

 character is a character which depends 

 upon the nature of the organism, while an 

 acquired character depends on the nature 

 of the stimulus. 



If we imagine a zygote to be a machine 

 capable of working out certain results on 

 material supplied to it, then we should 

 properly apply the term genetic character 

 to the features of the machinery itself, and 

 the words acquired character to the results 

 achieved by its working. These clearly 

 will depend primarily on the structure of 

 the machinery, and secondarily upon the 

 material and energy supplied to it — that is 

 to say, upon the way in which it is worked. 



Variations in genetic characters are vari- 

 ations in the machinery of different zygotes 

 that is to say, in the constitution— while 

 variations in acquired characters are vari- 

 ations in the results of the working of one 

 zygote according to the conditions under 

 which it is worked. 



For instance, let us take the case of those 

 twins which arise by the division of one 

 zygote, and are consequently identical in 

 genetic characters, i. e.,in constitution. If 

 they are submitted to different conditions, 

 they will develop diiferences which will de- 

 pend entirely upon the conditions and the 

 time of life when the differentiation in the 

 conditions occurred. These differences then 

 will be a function of the external conditions, 

 i. e., of the manner in which the machinery 

 is worked, and constitute what we call vari- 

 ation in acquired characters. 



ARE ACQUIRED CHARACTERS TRANSMISSIBLE 

 AS SUCH IN REPRODUCTION ? 



To return to our question, are the so- 

 called acquired characters ever transmitted 



