DIFFERENTIATION, MIGRATION, AND MIMICRY. 383 



he deduces, a priori, the impossibility of characters acquired by 

 the body being transmitted through the germ-plasm to the off- 

 spring. From this he implies that where we find no intelligible 

 mechanism to convey an imprint from the body to the germ, 

 there no imprint can be conveyed. Komanes has brought forward 

 many instances which seem to contradict this theory, and Herbert 

 Spencer remarks that " a recognised principle of reasoning — ' the 

 law of parsimony' — forbids the assumption of more causes than 

 are needful for the explanation of phenomena. We have evi- 

 dent causes which arrest the cell multiplication, therefore it is 

 illegitimate to ascribe this arrest to some property inherent in 

 the cells." 



With regard to the reduction or disappearance of an organ, 

 he states "that when natural selection, either direct or reverse, is 

 set aside, why the mere cessation of selection should cause de- 

 crease of an organ, irrespective of the direct effects of disease, I 

 am unable to see. Beyond the production of changes in the size 

 of parts, by the selection of fortuitously arising variation, I can 

 see but one other cause for the production of them — the compe- 

 tition among the parts for nutriment. . . . The active parts are 

 well supplied, while the inactive parts are ill supplied and 

 dwindle, as does the arm of the Hindu fakir. This competition 

 is the cause of economy of growth — this is the cause of decrease 

 from disease." 



I may illustrate Mr. Herbert Spencer's remarks by the fami- 

 liar instance of the pinions of. the Kakapo (Stringops) — still 

 remaining, but powerless for flight. 



As for acquired habits, such as the modification of bird 

 architecture by the same species under changed circumstances, 

 how they can be better accounted for than by hereditary trans- 

 mitted instinct, I do not see. I mean such cases as the ground- 

 nesting Didunculus in Samoa having saved itself from extinction 

 since the introduction of cats, by roosting and nesting in trees ; 

 or the extraordinary acquired habit of the Blackcap in the 

 Canaries, observed by Dr. Lowe, of piercing the calyx of Hibiscus 

 rosa- sinensis- -an introduced plant — to attract insects, for which 

 he quietly sits waiting. So the lying low of a covey of Partridges 

 under an artificial Kite would seem to be a transmitted instinct 

 from a far-off ancestry not yet lost; for many generations of 

 Partridges, I fear, must have passed since the last Kite hovered 



