380 SCOTT. [Vol. V. 



arguing against the idea of a vital force, he says : " The latter, 

 [i.e. the ontogenetic vital force] is no longer admitted by any- 

 body, now that we have turned from mere speculation to the 

 investigation of nature's processes; nevertheless its non-exist- 

 ence has not been demonstrated, nor are we yet in a position to 

 prove that all the phenomena of life must be traced to purely 

 physico-chemical processes, to say nothing of our actually being 

 able to so trace them " (No. 58, p. 643). 



In his later papers, Weismann admits that the germ-plasm may 

 be modified in various ways. " It must be admitted that there are 

 cases, such as the climatic varieties of certain butterflies, which 

 raise some difficulties against this explanation. I, myself, some 

 years ago, experimentally investigated one such case, and even 

 now I cannot explain the facts otherwise than by supposing the 

 passive acquisition of characters, produced by the direct in- 

 fluence of climate" (No. 57, p. 99). " I am at present inclined 

 to believe that Professor Vines is correct in questioning whether 

 sexual reproduction is the only factor which maintains Metazoa 

 and Metaphyta in a state of variability " (No. 60, p. 322). We 

 have, indeed, abundant evidence that food, temperature, moisture, 

 salt, and the like may have a profound influence upon the germ- 

 plasm, and though we can form no conception of the way in 

 which the amount of salt in the water will change Artemia into 

 Branchipns, or the quantity of food will determine the proportion 

 of the sexes in tadpoles, or how the change of food-plant meta- 

 morphosed the Texan species of Saturnia into something very 

 different (see Moritz Wagner, No. 55, pp. 307-310), yet we are 

 not impelled to take refuge in an appeal to unknown forces. Nor 

 can the well-known influence of the germ-glands upon the body 

 be explained in the sense of determining just how and why the 

 effect is produced. If the presence of the germ-glands can so 

 profoundly affect the soma, why should the converse influence 

 appear so incredible ? Still more mysterious is the influence 

 exerted upon the maternal organism by the spermatozoa (or per- 

 haps the foetus), so that the offspring by later sires often show 

 characters of previous sires. Virchow pronounced the stig- 

 mata of Louise Lateau to be "either fraud or miracle," but 

 the recent investigations in hypnotism show that the case may 

 be explained without accepting either horn of the dilemma. 

 Whether acquired characters be transmitted or not, it is cer- 



