PRELIMINARY DISCOURSE 13 



attend to the exhibit of the animals which I called invertebrate, 

 on account of the absence in them of a vertebral column. My re- 

 searches on these numerous animals, the accumulated observations 

 and facts, and finally the increased knowledge of comparative anatomy 

 which I gained from them, soon inspired me with the highest interest 

 in the subject. 



The study of invertebrate animals must, in fact, be of special interest 

 to the naturalist for four reasons : — (1) The number of the species 

 of these animals in nature is much greater than that of vertebrate 

 animals. (2) Since they are more numerous, they are necessarily 

 more varied. (3) The variations in their organisation are much 

 greater, more sharply defined and more remarkable. (4) The order 

 observed by nature in the successive formation of the different organs 

 of animals is much better expressed in the mutations which these 

 organs imdergo in invertebrate animals. Moreover, their study is 

 more fertile in helping us to imderstand the origin of organisa- 

 tion, with its complexity and its developments, than could possibly 

 be the case in more perfect animals such as vertebrates. 



Convinced of these truths I felt that, in the instruction of my 

 pupils, I should not plunge into detail straight away, but should 

 above all show them the general principles which hold good of all 

 animals. I tried to give them a view of the whole and of the essentials 

 which appertained to it, with the intention of taking subsequent 

 note of the main groups into which that whole appears to be divided 

 for purposes of comparison and more intimate knowledge. 



The real way, no doubt, of acquiring a thorough knowledge of an 

 object, even in its smallest details, is to begin by inspecting it in its 

 entirety. We should examine first its bulk, extent, and the various 

 parts which compose it. We should enquire into its nature and 

 origin, and its connection with other known objects. In short, we 

 should enquire into the general principles involved, from all possible 

 points of view. The subject is then divided into its chief parts for 

 separate study and examination in all the bearings likely to be in- 

 structive. By further dividing and sub-dividing these parts, and 

 inspecting each successively, we arrive at the smallest, where we do 

 not neglect the least details. Once these researches finished, the effects 

 have to be deduced from them, so that httle by little the philosophy 

 of science is estabhshed, modified and perfected. 



It is by this method alone that human intelhgence can gain know- 

 ledge (in any science) that is at once vast, solid and coherent. It 

 is solely by this kind of analysis that science makes real progress, 

 so that allied objects are never confused, but can be perfectly 

 known. 



