70 ZOOLOGICAL PHILOSOPHY 



caused extensive variations in them by the different environments 

 provided by the waters, nature led them little by Httle to the habit 

 of living in the air, first by the water's edge and afterwards on all 

 the dry parts of the globe. These animals have in course of time 

 been profoundly altered by such novel conditions ; which so greatly 

 influenced their habits and organs that the regular gradation which 

 they should have exhibited in complexity of organisation is often 

 scarcely recognisable. 



These results which I have long studied, and shall definitely prove, 

 lead me to state the following zoological principle, the truth of which 

 appears to me beyond question. 



Progress in complexity of organisation exhibits anomalies here and 

 there in the general series of animals, due to the influence of enviromrient 

 and of acquired habits. 



An examination of these anomalies has led some to reject the obvious 

 progress in complexity of animal organisation and to refuse to recognise 

 the procedure of nature in the production of living bodies. 



Nevertheless, in spite of the apparent digressions that I have just 

 mentioned, the general plan of nature and the uniformity of her pro- 

 cedure, however much she varies her methods, are stiU quite easily 

 distinguished. We have only to examine the general series of known 

 animals and to consider it first in its totaUty and then in its larger 

 groups ; the most unequivocal proofs will then be perceived of the 

 gradation which she has followed in complexity of organisation ; a 

 gradation which should never be lost sight of by reason of the afore- 

 mentioned anomalies. Finally, it will be noticed that whenever there 

 have been no extreme changes of conditions, that gradation is foimd to 

 be perfectly regular in various portions of the general series to which 

 we have given the name of famiUes. This truth becomes still more 

 striking in the study of species ; for the more we observe, the more 

 difficult, complicated and minute become oiu: specific distinctions. 



The gradation in complexity of animal organisation can no longer 

 be called in doubt, when once we have given positive and detailed 

 proof of what we have just stated. Now since we are taking the 

 general series of animals in the opposite direction from nature's actual 

 order when she brought them successively into existence, this grada- 

 tion becomes for us a remarkable degradation which prevails from 

 one end to the other of the animal chain, except for the gaps arising 

 from objects which are not yet discovered and those which arise 

 from anomalies caused by extreme environmental conditions. 



Let us now cast an eye over the complexity and totahty of the animal 

 series, in order to estabhsh positively the degradation of organisation 

 from one extremity to the other ; let us consider the facts presented 



