ORIGIN OF DIF1 ERKS II \ 



We do not intend to dispute entirely the action of natural selection and 



the influence of the Btruggle for existence, but simply to deny the applicability 



of tin- law t<> the more important modifications ami series <>t' modifications which 



occurred in tin- history of animals, taking the fossil Cephalopoda a- a type. 



We have in former papers conceded the preservation uf differentials to the law 



of natural selection, rather on account of the apparent logical necessity of thus 



:it iuur for the invariability of minute differences, like the ventral position of 



phon, the si phonal collar, the Bhoii funnel, tin- convexity of the Bepta and 



ventral lobe of Ammonoids, and the divergence <>r the type from tin- common 



S'autiloids which these characteristics indicated, rather than from any 



firm conviction derived from analytical study. 



We think iu>w that tin- changes in the surroundings acted upon the p] 



ism, inducing it to make efforts to accommodate it-elf to new conditions. 



Effort, being i reaction from within upon a common organization, necessarily 



similar series of modifications whenever the surroundings were not 



chang ipletelj a- to lead the phylum away from the original type on 



i - parallelisms occurred between the d inert? n- 



\ tiloidea and Ammonoidea, they were h--< apparent in Belemi 



which are more remote in habitat, and may be said to have been almost wholly 



in Sepioids, which are still more remote in habitat, as pointed out above. 



I ing that the differentials are in many cases new modifica- 



and, it' our position is true, they ;ire adaptive characters, correlative in the 



Nautiloids with their mixed hal rimmers and crawler-, in the Ammonoids 



with then habitat as reptant forms, in the Belemnoids with their intermediate 



im swimmers, and in the Sepioids with their habitat as 



surface swimmers, The simple lobes and Baddies, keelless abdomens, and ab- 



in tic- shells of the Nautiloids, the dendritic or deeper lobes 



; keels and rostra <>t the Ammonoids, the straight internal shell 



with its peculiar Belemnoids, and also the degenerate 



internal -hell or pen of the Sepioids, are plainly of this DatUl 

 working done upon a common organism could, of < se, no: | luce such re- 

 lent that it must have been assisted by the continuous action of 

 I lie law. therefore, a- referred to in tic 1 seems 



. that, in - - and habits an- similar, they probably produce 



lion or morphological equivalence between different series 01 forms 

 of the same type in the same habitat, and in bo far as they are different, they 

 ■ly produce the differentials which distinguish series and groups from 

 ■ 



than I ' 



