COLLECTED OBSERV ACTIONS ON BRITISH SAWFLIES. 89 



their true structure, in having shown that they are ))rojected 

 and everted wind-pipes, on which a flying membrane is spread, 

 in the same manner as skin on the projected ribs of a flying 

 dragon {Draco volans) or sail-cloth on the ribs of a windmill, 

 it will be useless to attempt the substitution of any other 

 term for that of wing. 



The beings then of which this paper treats possess an 

 exo-skeleton, or external skeleton, six legs, and either two, 

 four, or six wings, which are subject to metamorphosis, and 

 which arrive at perfection and maturity by one or other of 

 the following methods : — 



1. By passing through an amorphous state, — Amorpha, 

 — in which the penultimate state (or pupa, or chrysalis) is 

 provided with neither month nor organs of locomotion, 

 consequently it neither eats nor moves, nor does it bear any 

 resemblance to the perfect state. We find that the exo- 

 skeleton, after it has been shed for the last time, exhibits 

 some traces of the liberated imago, and that the various 

 portions, or plaits, or cases, are easily separated, and often 

 spontaneously dehised, the dehiscence taking place at 

 perfectly natural fissures. Although the limbs, notwithstand- 

 ing their change, and the divisions of the trunk are often 

 thus obviously indicated on the exterior surface of the 

 exo-skeleton, the penultimate cannot be said to bear any 

 resemblance to the ultimate state. This class contains 

 two subordinate classes or sub-classes, or as entomo- 

 logists, with apparently great impropriety, often call 

 them, " orders," a term which should be used, as it is in 

 places, for associating those animals that possess similar 

 natural characters, and have propensities in common : thus, 

 the Ferce amongst sucklers, the Accipitres amongst birds, 

 the Carnivores amongst Coleopiera, and Mantides amongst 

 Orthopiera, are really natural orders, and precise equivalents 

 one of the other; and each has an aquatic section, also 

 equivalents of each other. This group, then, is divided 

 into two minor groups by the number and clothing of the 

 wings, thus — (a) Lepidoptera, in which the imago has four 

 wings, all of them covered with scales, (b) Diptera, in which 

 the imago has two wings only, and these are generally naked, 

 but sometimes sparingly covered with hairs, or more or less 

 seldom with scales: m Diptera there are also two poisers, which 

 seem the representative of a second pair of wings, but this is 

 only a matter of opinion ; I am unable to prove them to be 

 so ; they possess, moreover, a pair of winglets, or lobes, one 



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