36 CLASSIFICATION. 



mouth (and the habits of the animals), having nothing 

 in common." 



We must, indeed, in my opinion, separate them 

 entirely from one another ; and I have proposed for 

 the group comprised in the old genus Podiira the term 

 CoLLEMBOLA, as indicating the existence of a projection 

 or mammilla enabling the creature to attach or glue 

 itself to the body on which it stands. 



We now come to consider whether this group should 

 be classed among the Insecta, or whether Lamarck was 

 right in separating it from that great class. Taking 

 each of the characteristic points separately, we begin 

 with the absence of metamorphoses. To this we must 

 not attribute too much importance. There are species 

 of Orthoptera and of Neuroptera which are almost in a 

 similar position. So, again, as regards the absence of 

 wings, the same argument holds good : in all orders of 

 insects there are wingless species. Moreover, although 

 it may seem paradoxical to say so, the character of an 

 organ is of greater classificatory value than the absence 

 of it. Thus, for instance, we have cattle and deer 

 without horns, but no cows have deer's horns or vice 

 versa. So the presence of four wings is absolutely 

 peculiar to the Insecta ; but some insects have only 

 two wings, and in all the large orders there are species 

 without any wings at all. The absence of wings is 

 therefore no conclusive evidence against classing the 

 CoLLEMBOLA amongst the Insecta. 



The absence of trachese is more significant. That 

 of wings involves only inability to fly, but that of 

 trachea3 implies that respiration is carried on in a 

 different manner. The importance, however, of the 

 difference is reduced to a minimum, because there are 

 no other special organs for respiration, and the process 

 seems to be carried on through the skin. Moreover, 

 while Papirius, like most of its allies, has no trachea, 

 SmyntJmrus has a well-developed system. I know 

 hardly any other case of species, so closely resembling 

 one another in other respects, differing so entirely as 



