400 OUTLINES OF EVOLUTIONARY BIOLOGY 



attacked the new-comers on their first arrival, they might have 

 exterminated them with little trouble and prolonged for an 

 indefinite period the life of their own race. Unfortunately for 

 themselves, however, they had lost the art of self-defence. Owing 

 to the absence of competition they had, in this respect at any 

 rate, undergone degeneration. Killing was actually forbidden 

 by their laws, and peace had reigned too long and too securely to 

 give place at once to war when the emergency arose. 



Just as the flightless birds of New Zealand have more or less 

 completely disappeared since the advent of carnivorous mammals, 

 so the Morioris, their happy isolation once broken, fell an easy 

 prey to the more virile Maoris. The latter proceeded to parcel 

 out the conquered country amongst themselves, claiming not 

 only the land but also the inhabitants thereof, many of whom 

 were massacred under circumstances of unutterable atrocity, 

 while the remnant were speedily reduced to the condition of 

 slaves. Under the changed conditions which had suddenly arisen 

 in their environment the Morioris were no longer fit to survive 

 in the struggle for existence, they had become degenerate in a 

 vital respect, and natural selection, as soon as opportunity arose, 

 stepped in and eliminated them. 



It would be easy to multiply illustrations of the great generaliza- 

 tion that when removed from the struggle for existence all 

 organisms tend to become degenerate, the organs or faculties 

 which they no longer require atrophying and gradually dis- 

 appearing for want of employment. We see this very clearly in 

 the case of sedentary animals such as the ascidians (Figs. 129, 

 130). The young ascidian is a highly organized creature which 

 swims actively about by means of a muscular tail, in the same 

 way as the tadpole of a frog. Like the latter it has nervous 

 system, notochord and sense organs though the sense organs 

 are of a type peculiar to itself and is an undoubted chordate. 

 It never, however, progresses further in organization, so as to 

 attain the true vertebrate condition. On the contrary, it gives up 

 its active life and withdraws as far as possible from the struggle 

 for existence by fixing itself to some rock or seaweed and envelop- 

 ing its entire body in a thick protective envelope, within which 

 it undergoes extensive degeneration. The tail and notochord 

 completely disappear, so do the sense organs, none of these 

 being any longer required under the new conditions of life. The 



