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THE AMERICAN NATURALIST [Vol. XLIII 



We must admire the durability of the good old inheritance 

 of acquired characters problem, even if its repeated resuscita- 

 tion is sometimes a little less than interesting to us. However, 

 our lessening of interest in it in no way reflects any lessening 

 of its importance. It is still the crux of the whole species- 

 forming problem. Neither mutations-theory nor Mendelism 

 make its solution any less imperatively needed. 



A recent important contribution, not of discussion alone but 

 of new facts, to the inheritance of acquired characters problem 

 is that of Jennings, who finds that, contrary to the admission 

 on theoretical basis of even some of the most thoroughgoing 

 anti-Lamarckians, acquired characters are not inherited in 

 the Protozoa; at least in those Protozoa which were the sub- 

 jects of Jennings's brilliant observation and experimentation. 

 This may be a serious blow to the neo-Lamarckian side of 

 the case — or it may not. It is if the old statement of the 

 problem is to be always adhered to, but for some time now 

 this statement has been recognized to be faulty and outworn. 

 The neo-Lamarckian, taking the aggressive, prefers to put 

 it this way: How are we to explain the fact that heritable 

 differences distinguishing species or constant varieties (ele- 

 mentary species?) are often identical with those differences, un- 

 inherited, which can be produced ontogenetically among indi- 

 viduals of a single species of the group by submitting them to 

 varying environmental or nutritional conditions ? The fact ex- 

 ists and th- presumption that it raises is that these identical 

 species (heritable) differences have had the same ultimate 

 causes which under our very eyes produce the non-heritable 

 differences of the ontogenic varieties. 



What is needed is the mechanism of cumulation or conversion of 

 the non-heritable differences into identical heritable ones. This 

 mechanism must, of course, concern itself with reproduction, 

 with the germ-cells; and put as Jennings strongly puts it, it 

 seems at first sight as if it must be an impossibly complex 

 mechanism. But after all it. is the change that has to be com- 

 plex. The mechanism needed is one capable of producing 

 changes of seeming great complexity. But comparatively sim- 

 ple mechanical transformers that produce very complex physio- 

 logical changes are not unknown in biology, and there may, 

 after all, be one awaiting discovery by Jennings, or some other 



