PREFACE. xxxiii 



the craw-fish of the ' Mammoth Cave,' and numerous insects and 

 arachnidans). 



Lepidopus, Trichiurus, Stromateus, exemplify fishes which lose 

 the ventral fins entirely with age ; they are rudimental in Gem- 

 pylus, Psettus and Centronotus ; Soleotalpa has only the right 

 ventral developed and the left rudimental ; the pectoral fins are 

 rudimental in many pleuronectoids, either on both sides, as in 

 Buglossus and Achirus, or on the blind side only, as in Monochir 

 and many species of Synaptura. The ' adipose fin ' of certain 

 Siluroid and Salmon oid fishes is a rudimental dorsal, sometimes 

 showing traces of rays. 



The prevalence of birds in New Zealand without wings {Dinor- 

 nis), or too feebly developed for the purpose of flight (Apteryx, 

 Brachypteryx, Notornis, &c), is associated with the absence in 

 those islands of any higher form of life exercising destructive 

 mastery of organisation, until the immigration of the human race. 

 The wings of such birds, like the eyes of the cavern fishes and 

 crustaceans, would seem to have degenerated for want of use ; 

 their legs, by which locomotion was exclusively exercised, to have 

 gained in size and strength. 



Lamarck, 1 adverting to observed ranges of variation in certain 

 species, affirmed that such variations would proceed and keep pace 

 with the continued operation of the causes producing them ; that 

 such changes of form and structure would induce corresponding 

 changes in actions, and that a change of actions, when habitual, 

 became another cause of altered structure ; that the more frequent 

 employment of certain parts or organs leads to a proportional 

 increase of development of such parts, and that as the increased 

 exercise of one part is usually accompanied by a corresponding 

 disuse of another part, this very disuse, by inducing a proportional 

 degree of atrophy, becomes an added element in the progressive 

 mutation of organic forms. 



Concomitant changes of climate, and other conditions of a coun- 



1 Philosophic Zoologicpie, torn. i. chaps, iii. vi. vii. 

 VOL. I. b 



