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 of a 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, ovnngto peculiar necessities of individual struc- 

 ture, two or more of these are confluent, as often occurs in the analogous 

 vertebral axis of Vertehrata* 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.-)- 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 

 DynastidcR or PrionidcB; 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 generaHze, my own 



* The number of vertebrae, however, in the axis of the Vertehrata has a 

 much greater tendency to vary than the number in the vertebral axis oi Annu- 

 losa. So far, as well as in being more complicated, the skeleton of the Annu- 

 losa is superior to that of the Vertehrata. 



■j- I may here give, as an example, my own observation on the abdomen of 

 an Oryctes, as mentioned in " Horce Entomologirw," Vol. 1, p. 412. 



