344 



THE 



ATURALIST [Vol. LI 



doubted that the complex mechanism of mitosis rests 

 upon definite structural machinery, established by long 

 periods of evolution. 



In order to account for the ditferentiation of cell-nature 

 which occurs in ontology, Weismann was led to assume 

 a thoroughgoing differential se<>reft-ation of the biophores 

 of the orm-mal o-oi'm-cell in the course of eml)ryological 

 deveIoi»m(^Tit : iii other words, he supposed that in this 

 process the rule ot mirlea)- dix ision is ditterentiation and 

 not re(hi|»Iicati(iii. I hi> a>>iittiption, although undoubt- 

 edlv a jtarlial truth, r^ neither necessary nor in harmony 

 with uciieral ln(.h)mral ]tr<.lial>iiities, in the form in which 

 it was made W ei-matm.' ■ ( onsequently the difficulties 

 into which it lias h^d liis u'enei'al theory, can be regarded 

 as without important bearing upon the acceptability of 

 corpuscular hypotheses at large. 



Since redu])licating division is the established rule 

 nmonu- uniceihilar oro-ariisms-which must liave had a 

 h)im ( \..hiti(maM iM..i\ ^\ . -hiuihl expect tlii- lule to 

 ite ceii^t r\-ei] a- tar a- jMt-Hhh' iii iiiiiltieellular evolution. 

 VmohIiii- t(. Ih. 11. lal hi \ Ml H apilulation. th'- should 

 he.-p ll\ tun Iwi th< pninaix M ^ ..t (.ntno(Mi> , for 



app.ai^ ..ltd! 1n'h..hl ' 'I IK hhiMiihi' ii'ix he ^mply 



an nnditrduitiated ma- ot uenn(elN, anah.uou- to a 

 homogeneous colon v of unicelluhir forms. Kudinientary 

 differentiation mav ])e Irrouulit about and deternuned 

 by specific enzyme constitution, without differential ])ar- 

 titionment of enzvmes m x uinentation, since the forces 

 acting upon an\- cell imi>t (h'petid iii)on its ijosttion in the 

 mass, and the actiwitioii or mliihition of a ffiven enzyme 

 may l)e conditioned l.\ the ))r(-eiice ol definite stimuli in 

 definite inten-itie- T\ \- im iii_ the i a-e in\ (ell could 

 assume germinal <li.n.i<tM^ I ^Mhr.d Imu, il total 



