Thorax in winged Insects. 151 
Jast number of segments. I even stated some strong arguments for think- 
ing that the Ametabola and Arachnida might be reduced to the annulose 
type of form. Such was the state of the subject when I left it. Inow 
therefore proceed to M. Audouin’s general theory of the insect skeleton, 
which is the same precisely as mine, although, from his taking no notice 
of my work in the *‘ Annales des Sciences Naturelles,” I must suppose he 
never saw it. Bya cautious process of induction he says that he has 
arrived at the following important conclusions, viz. 
Ist. That the skeleton of annulose animals is formed of a determinate 
number of parts, which are either distinct or confluent, as may be, but 
which exist generally in all. 
2ndly. That in some cases a part will be diminished, or even will 
disappear, while in others the same piece will undergo an extraordinary 
developement. 
3rdly. That the developement of one piece exerts an inverse influence 
on the contiguous pieces, whence arise the principal differences so much 
relied upon in classification. 
With respect to these three results I may observe, that they are in 
perfect accord with the “Hore Entomologice.”’ I had already in that work 
stated the determinate number of primary segments to which the Verte- 
bral Axis of all annulose animals tended, and as to M. Audouin’s second 
conclusion, it is nothing more than another mode of expressing the 
maxim of variation as applied to organs. His two leading observations, 
therefore, that the skeleton of Crustacea and Arachnida only differs from 
that of Winged Insects by the mode in which their segments are developed, 
and that the nnulosa generally only differ from each other in the deve- 
lopement of the same parts in each, or in the confluence or separation of 
these parts, are neither of them new, any more than the reduction of the 
larva and perfect insect to the same general law of structure. Where we 
differ is, as to the mode in which this reduction may be made, and I 
confess, after haying bestowed some attention on the subject, that I am 
inclined now to prefer the explanation given by M. Audouin. Our 
leading principles are, however, nearly the same, and in fact, as the 
study of the natural system is founded on the maxim of variation,* so that 
* The maxim of variation, a8 applied to the arrangement of the animal 
