PEOPLING OF LAND AND SEA 173 



formed complete and unrelated to the parts already existing 

 in the original Crustaceans. There is general agreement that 

 they were primitively respiratory organs. This, therefore, is 

 the question we have to determine : is there any respiratory 

 organ among the Decapod Crustaceans that can possibly be 

 compared with the wings of the Insects ? Such an organ 

 actually exists. We saw that the second segment of the leg of 

 these creatures bears an articulated branch like the foot itself, 

 known as an exopodite. The first segment likewise carries an 

 appendage, the epipodite, but this appendage is not articulated 

 and has the form of a lanceolate plate. It rises from below the 

 carapace in an upward direction, and usually bears branchial 

 filaments. It is therefore a respiratory organ. Let us suppose 

 that the carapace, the protecting shutter of the branchiae, 

 disappears with the branchiae, and thus leaves the epipodite 

 exposed ; and let us assume that the segment of the leg that 

 bears the epipodite grows and becomes one with the wall of the 

 body ; then the epipodite, mobile, and to some extent already 

 directed backward, will be carried back against the dorsal 

 surface, just where wings are situated. It is exceedingly likely, 

 therefore, that these organs were originally respiratory 

 accessories of the feet — epipodites — which became wings by 

 a change of function when the carapace disappeared. The 

 ' beating " of these accessories probably had no other object 

 in the first place than to renew the air around the Insect and 

 to assist its respiration, which, on account of the aerial tracheae, 

 had become very intense. Hence the wing is no new organ, but 

 a pre-existing one adapted to another function. Without this 

 organ, Insect-flight would never have been achieved ; it could 

 be regarded, therefore, as a preadaptation for flight, and this 

 simple deduction suffices to indicate how vague, inaccurate, 

 and elastic the word is, and how capable therefore of giving 

 rise to false interpretations. 



We have thus seen how the creation of the Insect was evolved. 

 The earliest, Neuroptera and Hymenoptera, were represented in 

 the Devonian Period. Even in the Silurian deposits something 

 very like a wing of Hemiptera has been found. In any case 

 the Carboniferous Period witnessed the appearance of huge 

 Ephemeridae, of Libellulae seventy centimetres in span, of 

 gigantic Phasmidae, precursors of the Termites, the Cicada, 

 Fulgoridae, and the existing Hemiptera, in which the body 



