SYSTEM OF NATURE. 
107 
Aptera very closely approach each other, by means of the 
Diptera and Anoplura ; so closely indeed, that, in the 
instance of more than one genus, it is difficult to say to 
which province it really belongs. This has led to the 
mixing up of these supposed primary divisions of the 
animal kingdom, — a mixing up not consequent on care¬ 
lessness or haste, but the result of deep consideration and 
cautious induction ; and I must in candour remark, that 
no author of celebrity, and scarcely one who has attempted 
a classification, has adopted Aristotle’s broad division of 
Pterota and Aptera. Linneus, Fabricius, Clairville, Cuvier, 
Latreille, Leach, Kirby and Stephens, dismiss the idea as 
even unworthy consideration. As it has always been my 
wish to quote the views of eminent zoologists, by way of 
corroborating my own, I must admit that this “ cloud of 
witnesses ” against me, — men whose opinions I should 
have quoted as almost presumptive evidence, if in my fa¬ 
vour, — throws a doubt over the proposed division of arti¬ 
culates which it is extremely difficult to dissipate. 
With respect to the other divisions of the invertebrate 
animals into Vermes Mollusca and Vermes Annelida, 
and into Radiata Echinodermata and Radiata Zoophyta, 
I think that zoologists generally will be inclined to ad¬ 
mit such or similar divisions. In the instance of the 
zoophytes it may, however, become a question for the mi¬ 
croscope to decide, whether the Amorphozoa or sponges 
are not distinct from the other Radiata. 
Before closing this chapter, which has already extended 
to an unreasonable length, it seems desirable to allude for 
an instant to the supposed fact mentioned at page 26, that 
the subnormal groups form a series among themselves. 
Thes6 subnormal groups, in the present instance, are the 
