SOME ASPECTS OP ZOOLOGY 55 



There is nothing inherently improbable in the theory that 

 the factors of the germ-plasm may be affected by chemical and 

 physical changes in the soma. Nor does it stand in contradic- 

 tion to the established principle that it is only germinal and 

 not somatic changes that are inherited. For we are now 

 postulating a germinal change, and that is all that is required. 



Tower claims that he has produced germinal changes in the 

 potato-beetle, mainly by the combined action of' heat and 

 moisture, such changes being evidenced by the excessive pro- 

 duction of mutants in the next generation. And there is other 

 evidence pointing in the same direction. 



But, after passing it in review, it must be confessed that the 

 available evidence on this point is insufficient, and we are still 

 ignorant of the causes which may produce changes in factors, 

 and still more ignorant of how new factors come into existence. 



All that we do know is that many of the factors that 

 operate in plants are chemical, and there is good reason 

 for believing that all the so-called " factors " are chemical 

 bodies, often of great complexity. Such highly complex 

 molecules may, under conditions not accurately known to us, 

 take up a fresh molecule of some element, and in so doing 

 entirely change their character. 



But such a hypothesis, though not improbable, is highly 

 speculative in the present state of our knowledge. I do not 

 propose to pursue the subject any further, beyond stating my 

 belief that factors are susceptible of change, by some means 

 not yet ascertained. 



Now that I have passed from the region of ascertained fact 

 to the borderland of speculation, I will conclude by indicating, 

 as briefly as possible, what definite lessons are to be learnt from 

 the biological researches of the past fifteen years. 



You will agree, I hope, that experimental zoology and 

 botany have picked up a number of new factors which so 

 modify earlier doctrines that we must reconsider the moral 

 and ethical standards founded on those doctrines. 



It has been my purpose — though I am afraid that I may 

 seem to have wandered a good deal from it — ^to urge that a 

 sound knowledge of zoological science is an indispensable 



