I A CHAPTEK IN DARWINISM 27 



of life ; whilst Elaboration is a gradual change of 

 structure in which the organism becomes adapted 

 to more and more varied and complex conditions of 

 existence. In Elaboration there is a new expression 

 of form, corresponding to new perfection of work in 

 the animal machine. In Degeneration there is sup- 

 pression of form, corresponding to the cessation of 

 work. Elaboration of some one organ may be a 

 necessary accompaniment of Degeneration in all the 

 others ; in fact, this is very generally the case ; and 

 it is only when the total result of the Elaboration of 

 some organs, and the Degeneration of others, is such 

 as to leave the whole animal in a lower condition, 

 that is, fitted to less complex action and reaction in 

 regard to its surroundings, than was the ancestral 

 form with which we are comparing it (either actually 

 or in imagination) that we speak of that animal as 

 an instance of Degeneration. 



Any new set of conditions occurring to an animal 

 which render its food and safety very easily attained, 

 seem to lead as a rule to Degeneration ; just as an 

 active healthy man sometimes degenerates when he 

 becomes suddenly possessed of a fortune ; or as Eome 

 degenerated when possessed of the riches of the ancient 

 world. The habit of parasitism clearly acts upon 

 animal organisation in this way. Let the parasitic 

 life once be secured, and away go legs, jaws, eyes, and 

 ears ; the active, highly-gifted crab, insect, or annelid 

 may become a mere sac, absorbing nourishment and 

 laying eggs. 



Eeference was made above to the larval stage of 



