154 Mr. W.S. MacLeay on the Anatomy of the 
From such facts we come to the conclusion that every one of the twelve 
segments composing the body ofa larva, I may say of an annulose animal, 
can carry instruments of locomotion or can be without feet, but that in 
caterpillars there are only six true feet, two to each of the three thoracic 
segments, Supposing true feet to be those of the imago, the last con- 
clusion may also be arrived at by dissecting any caterpillar just when it 
is about to change to the chrysalis state. 
The perfect winged insect in like manner consists of thirteen primary 
segments, although often, owing to peculiar necessities of individual strue- 
ture, two or more of these are confluent, as often occurs in the analogous 
vertebral axis of Vertebrata.* It may easily therefore be shewn that the 
differences which have been pointed out in respect to the number of seg- 
ments in perfect insects result more often from imperfect study or un- 
practised examination on the part of the person describing than from any 
real anomaly in the animal described.t This truth will be evident to any 
entomologist who takes the trouble of comparing the perfect insect with 
the pupa and this again with the larva. By means of the pupa we may 
always learn how the thirteen segments of the larva are disposed of in the 
perfect insect. Let any large beetle be taken, for instance one of the 
Dynastide or Prionide; at first sight it seems to have no more than 
eleven segments to the vertebral axis, but on more accurate examination, 
and particularly on comparing it with the pupa, we discover that in reality 
it has thirteen, that is, the number of the larva. This comparison must 
be attended to by all who wish to obtain correct ideas of the structure of 
an insect; and the error which has vitiated Mr. Kirby’s description of the 
thorax and abdomen, and which has induced him to describe so many dif- 
ferences which do not in reality exist, arises from his not having 
sufficiently studied the larva, and particularly the pupa state of insects. 
If my worthy friend however has erred in failing to generalize, my own 
* The number of vertebre, however, in the axis of the Vertebrata has a 
much greater tendency to vary than the number in the vertebral axis of Annu- 
losa. So far, as well as in being more complicated, the skeleton of the Annu- 
losa is superior to that of the Vertebrata. 
+ I may here give, as an example, my own observation on the abdomen of 
an Oryctes, as mentioned in “‘ Hore Entomologice,” Vol. 1, p. 412. 
