LECTUKE XXIV 



OBJECTIONS TO THE THESIS THAT FUNCTIONAL 

 MODIFICATIONS ARE NOT TRANSMITTED 



Giant stog as an example of co-adaptation or 'hai-monious adaptation' — This occurs 

 even in passively functioning parts — Skeleton of Arthropods — Stridulating organ of 

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

 form 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 Ricin 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 functionally acquired modifications. 

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

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

 other parts, and these latter must therefore have changed si-muUaneously 

 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 ligamentwm nuchai,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 variations 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 gi-oups of organs have in the course of evolution 



Digitized by Microsoft® 



