LECTURE XXIV 



OBJECTIONS TO THE THESIS THAT FUNCTIONAL 

 MODIFICATIONS ARE NOT TRANSMITTED 



Giant stag as an example of co-adaptation or 'harmonious adaptation' — This occurs 

 even in passivelj" functioning parts — Skeleton of Arthropods— Stridulating organ of 

 ants and crickets — Limbs of the mole-cricket — Wing-venatioii — Colorations which 

 foi'm mimetic pictures —Harmonious adaptations in worker-bees and ants — Degenera- 

 tion of their wings and ovaries — The quality of food acts as a liberating stimulus — 

 Vom Rath's case of drones fed with royal food — Transition-forms between females and 

 workers — Wasmann's explanation of these— The Amazon ants — Two kinds of workers 

 — Appendix : Zehnder on the case of ants — On the skeleton of Arthropods — Hering's 

 interpretation of Ehrlich's Eicin experiments — Hering's position in regard to the 

 transmission of functional modifications. 



It was Herbert Spencer, the English philosopher, who first 

 brought the argument of co-adaptation into the field against my 

 view of the non-inheritance of fuuctionall}^ acquired modifications. 

 He pointed out that many, if not, indeed, most modifications of bodily 

 parts, to be effective, implied further changes, often very numerous, in 

 other parts, and these latter must therefore have ch&nged simultaneously 

 with the part which was being changed under the control of natural 

 selection ; this, however, is only conceivable as due to an inheritance 

 of the changes caused by use, since a simultaneous alteration of so many 

 parts through natural selection would be impossible. If, for instance, 

 the antlers of our modern stag were to grow to the size of those of the 

 Giant Stag of the Irish peat- bogs, which measured over ten feet across 

 from tip to tip, this would mean — as has already been shown — a 

 simultaneous thickening of the skull, and to bear the heavy burden, 

 a strengthening of the ligamentum nuchw,oi the muscles of the neck and 

 back, of the bones of the legs and their muscles, and, finally, of all the 

 / nerves supplying the muscles ; and how could all this happen simul- 

 taneously with, and in exact proportion to the growth of the antlers, 

 if it depended — as natural selection assumes — on chance vai-iations of 

 all these parts ? What if the appropriately favourable variation in 

 one of these organs did not occur ? A harmonious variation of all 

 the parts — bones, muscles, nerves, ligaments— which unite in a com- 

 mon activity, is an inadmissible assumption, because, in many cases, 

 such co-operating groups of organs have in the course of evolution 



