RELATION BETWEEN HABIT AND STRUCTURE IN THE 

 INSECT WORLD 



/>'// Franl: /•.'. l.utz 



Wl'". ill' not know \\ 111 llici- ;iii iiiscci liiis ;i ,i;i\<'ii si iMictin'c ;is ;iii ;i(l:i|)- 

 lalioii to its li;il)its of life o|- wlictlici- tlic liahits li;i\c liccii dcxd- 

 o|)('(l to coiifofiii to cliimLjcd sti-uctiiiTs. l-'ollo\\ iiiii tlic work of 

 hai-wiii. most l)iolouists hclicxcd that tlic ^rcatci- iiuiiiImm- of st i-iictui-('s 

 ai-osc yi-adiially citlici- tlifoiioli the natiii'al selection of \ai-iatioiis fa\()i'al)lc 

 to a >;i\{'ii liahit of hy tlic eil'cct of use, and the tci-iii "adaptation" lias 

 come to imply as imieli. Specifically, this would mean that a fi'fasslioppef 

 has loni;- powcrfid hind Ici^s cither heeanse of the fact that its ancestors 

 with the longest, st fonyest hind le^s wei'c the licst jtimpcfs and so wcfc 

 most siicecssfiil. of thfotiiih continued use hy its anccstofs of their hind 

 legs for jumping. 



Til this coiincction two things must he said. First, not a single instance 

 ol the iiihcfitaiicc of the cU'ect of nsc or distise upon anatomical characters 

 has cx'cr heen exjjcrimentally pi-oxcd, while there arc inimeroiis cases of 

 experimental ncgati\-e <'\idcncc. Second, in recent years many cases ha\-e 

 been recorded of larg( heritahle \ariations arising suddenly. .Vmong these 

 is that of ahnormally larye hind legs in no less common an animal than the 

 domestic cat. Xow when these "ral)l)it cats" run they do so hy a scries 

 of lcai)s. '{'he large hind legs are not adapted (in the technical sense) to 

 jimipiim l)iit the hahit of jumping is adajjtcd to the large hind legs. .\ 

 cockroach's flat body enables it to lixc in cracks and cre\ices. If its body 

 were of snch shape that it could not, it would li\e elsewhere as its rclatixcs 

 do. Natural selection doubtless accounts for the failure of many \ ariations 

 to be perpetuated, but doubtless many \ariations are j)erpetuated either 

 because the eliminating action of natural selection is dodged by a change 

 of habits, that is by habit becoming adapted to structure; or because they 

 an- of neutral \aliu" fitting in with the habits of their possessors in the 

 struggle for existence — that is, natural selection does not efi'ect them at all. 

 There is another class of characters. 'I'hcy are very striking but no 

 use can e\er be imagined for them. To this class belong most of the pat- 

 terns of coloration, many of the horns and s|)ines, and the unusual develop- 

 ment of some parts of the body. These are explained a> lia\ ing come about 

 either through orthogenesis or the effect of the cn\ironmeut or in other ways 

 which are too comjjlcx to be mentioned here. If this be true, is it not 

 probable that some, at least, of the characters which are used by insects 



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