246 THE HISTORY OF CREATION. 



The correlative adaptation between the reproductive organs 

 and the other parts of the body deserves a very special con- 

 sideration, because it is, above all others, likely to throw 

 light upon the obscure and mysterious phenomena of in- 

 direct or potential adaptation, which have already been 

 considered. For just as every change of the sexual organs 

 powerfully reacts upon the rest of the body, so on the other 

 hand every important change in another part of the body 

 must necessarily more or less react on the sexual organs. 

 This reaction, however, will only become perceptible in the 

 formation of the offspring which arise out of the changed 

 .generative parts. It is, in fact, precisely those remarkable 

 and imperceptible changes of the genital system (in them- 

 selves utterly insignificant changes) — changes of the eggs 

 and the sperm — brought about by such correlations, which 

 have the greatest influence upon the formation of the ofi"- 

 spring, and all the phenomena of indirect or potential adapt- 

 ation previously mentioned may in the end be traced to 

 correlative adaptation. 



A further series of remarkable examples of correlative 

 adaptation is furnished by the different animals and plants 

 which become degenerated through parasitic life or para- 

 sitism. No other change in the mode of life so much 

 affects the shapes of organisms as the adoption of a 

 parasitical life. Plants thereby lose their green leaves ; as, 

 for instance, our native parasitical plants, Orobanche, La- 

 thrsea, Monotropa. Animals which originally have lived 

 freely and independently, but afterwards adopt a parasitical 

 mode of life on other animals or plants, in the first place 

 cease to use their organs of motion and their organs of 

 sense. The loss of this activity is succeeded by the loss of 



