4-'}^ ANN'I-.\I, ;;:-.r<M;T r-MITUSOXIAV IKSTTTTTIOX, 101S. 



to the preceding. S(.>ifosaurus. This animal had for its immediate 

 aii'.TStors bipeds like "he ance.-tors of Trieeralops. and, like Tricera- 

 lops. it became readapted to ouadrupedal life, nut \vhile the tri- 

 radiate pelvis of its far-away quadrupedal ancestors lias been physio- 

 logically reestablidied ihroiiirli regressive evolution (atrophy) of 

 poMpubis and ischium in Triceratops ( Dollo. 1. c. p. !-!-<>) these 

 {)art> have evolved iii ;i IK : \V direction in SLeir(-:anrii . Here the 

 i- chili in i)i'co!iir- * in'] II-I^IM! :, ii; S Hat leneil : tlie ]K>stpiib; ihe same 

 and moreoxer applies Ux-ir eiosely alonir tlie ventral in ii\a'in o[' the 

 ischiuin. l>ui moi'piioloii'ically tliere i- here no retn.rn to the former 

 triradiatc cinidition of the [)elvis. since th' i>chinm has kept some 

 I race of tlie form which it acquired in the biped pha-e. and liie |)O 

 terior I.' rand) - !' ! iu- j <-! \ i- i:- no Ioniser formed bv the iseh mm alone 

 hut b\' thi- eoinple.x. A\'hi!e ex-oh'inL! 1 'u: tlie new 



diieciion tin I hus changed in function (Dolio. !. c. p. 



i IT ). 



We find an i'lnsl! :it;on of llu v firs! alternative of (lie thinl law in 

 the evolution of the arm?: in the Octopods. 'These anima is in adaj)t- 

 inii 1 tliem>elve.- to i a pair of arm.- (t lie tentac- 



ular arm-) ; iiale ancestors (he heteropod de- 



capods. M. ; L'oine i>opod> autam (exc( : [)(rni!.* I lie pecu- 



liar cas< ctocotylisation <d one of its 



arm-) like theii '- tlie iH-K^nnotenthids (isopod de- 



eapod:- i \'^i : -' 1 he same number of arms 



(see Dollo. i 



The best tion for the second alternative of the third hnv is 



the foot >! ilagns. an arboreal IvMn.ii'ai'oo. The si r net u re of 



the fool in the ial Macropodidae- the predominance of the 



fourth to second and third, the reduction of 



ihe lil'i', li ipearance of the ii'reat toe slio\\"s us 



thai \\i.M'e arboreal. In Dendrolainis, a 



Maci'opni arboreal, llie opposable ti'roat 



toe. co!,; : diaie ancestors t!ic terrestrial 



kaiiii'ai I !.!. i>iit the unreduced |)arts of 



the I' l'i n^' evolution ni :< new direction. 



\\'iii!" i he in. i ii : iminished in length, 



ihe- ph;i e ieniilhened and tiie chnvs !ia\e 



;! 1 the same time ! Tim- the font of Dendroiairus has 



tioi bei r i rucl me of the foot ol il> distant 



icci :i 11 v flu" 

 I litmtfifirnini* afriratm*. in I'I 



