DEFINITION OF THE TERM INSECT. 25 
legs and a change of form only; in the Orthoptera, He- 
miptera, &c. in the mere acquisition of wings; in the 
Libellulina, in the loss of the mask that covers the mouth 
and the acquisition of wings; in the Diptera, in the ac- 
quisition of six legs, wings, a change of the oral organs 
and of the form; in some of the Octopods (Acarus, L.), in 
the acquisition of a pair of legs; and in others (Phalan- 
glum and Aranea, L.), solely in a modification of them 
as to their proportions; in the Myriapods, the alteration 
that takes place in this respect is considerable; a large 
number of pairs of legs is acquired and many additional 
abdominal segments, and the proportion which the ab- 
domen bears to the whole insect is quite altered. In all 
these cases there is a change more or less, either partial 
or general, of the original shape or organs of the animal; 
and with regard to their metamorphosis, there is a greater 
difference between a young and adult Jus than between 
a young and adult grasshopper or bug: so that if the me- 
tamorphosis, per se, be assumed as a principal regulator 
of the class, the grasshopper or bug have as little claim 
to belong to it as the Zulus. 
M. Lamarck lays considerable stress upon another 
character—That Jnsecta engender only once in the course 
of their lives, and Arachnida more than once. But this, 
if examined, will be found to be confined chiefly to the 
Pulmonary Arachnida, the Tracheans following the law 
of Insecta in this respect?. 
You may perhaps object that the bringing of the Tra- 
chean Arachnida and the Myriapoda into the class In- 
secta will render the approximation of them to a natural 
* Male Znsecta in some instances engender more than once. Mr. 
Macleay sen. has observed this with regard to Chrysomela Polygoni, 
and I have noticed it in Bombyx Mori. 
