CAUSES OF TIIK I'iM.NoMi 



individual (Jomatufa is the llydrozoic stock plus all the M*> 



<lt(x<t' vvliicli proceed from it. 



No doubt it sounds paradoxical to speak of u mill: 

 Aphides, for example, as parts of one m i J.IIM!..^;, ;i | ;,,.. 

 ual ; but beyond the momentary shock of th- 

 harm is done. On the other hand, it the asexual J/ 

 are held to be individuals, it follows, as a logical con- 

 not only that all the polyps on a Cordylophora tn-i- are 

 " feeding individuals," and all the genital sacs itivo 



individuals," while the stein must be a " stump individual," 

 but that the eyes and legs of a lobster are "ocni 

 "locomotive individuals." And this conception i> not ,-nly 

 somewhat more paradoxical than the other, but suggests a 

 conception of the origin of the complexity of animal >truct- 

 ure which is wholly inconsistent with fact. 



IV. ^ETIOLOGY. 



Morphology, distribution, and physiology, investigate and 

 determine the facts of biology. ./Etiology has for its ol 

 the ascertainment of the causes of these facts, and th 

 planation of biological phenomena, by showing that \ 

 stitute particular cases of general physical laws. It is hardly 

 needful to say that aetiology, as thus conceived, is in ii> in- 

 fancy, and that the seething- controversies, to which 

 attempt to found this branch of science made in the "Or 

 of Species" has given rise, cannot IMJ dealt with in this place. 

 At most, the general nature of the problems to be solved, and 

 the course of inquiry needful for their solution, may be indi- 

 cated. 



In any investigation into the causes of the phenomena of 

 life, the first question which arises is, Whether we have any 

 knowledge, and if so, what knowledge, of the origin of living 

 matter ? 



In the case of all conspicuous and easily-studied organ- 

 isms, it has been obvious, since the study of Nature bojran, 

 that living beings arise by generation from living beinr. 

 a like kind; but, before the latter part o; ntet -nth 



tury, learned and unlearned alike shared the convict 

 this rule was not of universal application, and that mult it 

 of the smaller and more obscure organ i-; 



the fermentation of not-living, and especially of putrefying 

 dead matter, by what was then termed genera* -oca 



or spontanea, and is now called abioyenetis. Redi showed 



