ADDRESS. Ixxi 



takes place. Some experiments of Dr. Child's, communicated to the lloyal 

 Society during the last year, again throw douht on the negative results 

 obtained by M. Pasteur ; so that the question may be not finally determined, 

 but the balance of experiment and opinion is against spontaneous generation. 



One argument presented by M. Pasteur is well worthy of remark, viz. that 

 in proportion as our means of scrutiny become more searching, heterogeny, 

 or the development of organisms without generation from parents of similar 

 organism, has been gradually driven from higher to lower forms of hfe, so 

 that if some apparent exceptions still exist they are of the lowest and 

 simplest forms, and these exceptions may probably be removed, as M. Pasteur 

 considers he has removed them, by a more searching investigation. 



If it be otherwise, if heterogeny obtains at all, all wiU now admit that at 

 present the result of the most careful experiments shows it to be confined to 

 the most simple organic structures, such as vibrions and bacteria, and that all 

 the progressive and more highly developed forms are, as far as the most en- 

 larged experience shows, generated by reproduction. 



The great difficulty which is met with at the threshold of inquiry into the 

 origin of species, is the definition of species ; in fact species can hardly be 

 defined without begging the question in dispute. 



Thus if species be said to be a perseverance of type incapable of blending 

 itself with other types, or, which comes nearly to the same thing, incapable 

 of producing by union with other types oflPspring of an intermediate cha- 

 racter which can again reproduce, we amve at this result, that whenever 

 the advocate of continuity shows a blending of what had been hitherto 

 deemed separate species, the answer is, they were considered separate species 

 by mistake, they do not now come under the defiuition of species, because 

 they interbreed. 



The line of demarcation is thus ex hypothesi removed a step further, so 

 that, unless the advocate of continuity can, on his side, prove the whole 

 question in dispute, by showing that all can directly or by intermediate 

 varieties reproduce, he is defeated by the definition itself of species. 



On the other hand, if this, or something in fact amounting to it, be not 

 the definition of species — if it be admitted that distinct species can, imder 

 certain favourable conditions, produce intermediate offspring capable of re- 

 production, then continuity in some mode or other is admitted, j 



The question then takes this form. Are there species or are there not ? 

 Is the word to be used as signifying a real, natural distinction, or as a mere 

 convenient designation applied to subdi\isions having a permanence which 

 ■wiU probably outlive man's discussions on the subject, but not an absolute 

 fixity? The same question, in a wider sense, and taking into consideration 

 a much longer time, would be applicable to genera and families. 



Actual experiment has done little to elucidate the question, nor, imless we 

 can suppose the experiments continued through countless generations, is it 

 likely to contribute much to its solution. We must therefore have recourse 

 to the enlarged experience or induction from the facts of geology, palaeon- 

 tology, and physiology, aided by analogy from the laws of action which 

 nature evidences in other departments. 



The doctrine of gradual succession is hardly yet formularized, and though 

 there are some high authorities for certain modifications of such view, the 

 preponderance of authority would necessarily be on the other side. Geology 

 and palaeontologj' are recent sciences, and we cannot teU what the older 

 authors would have thought or written had the more recently discovered 

 facts been presented to their view. Authority, therefore, does not much help 

 us on this question. 



