174 



HINTS ON THE ANCESTRY OF INSECTS. 



202. Foot ofChiro 

 nonius. 



claws, as seen in aquatic larvae, such as Chironomus (Fig. 202), 

 Ephydra (Fig. 203 a, b, c, pupa) and many others. As the Proto- 

 leptus assumed a terrestrial life and needed to walk, the rudi- 

 mentary feet would tend to elongate, and in consequence need 

 the presence of chitine to harden the integument, until the habit 

 of walking becoming flxed, the necessity of a jointed structure 

 arose. After this the different needs of the offspring of such an 

 iusect, with their different modes of taking 

 food, vegetable or animal, would induce the 

 diverse forms of simple, or raptorial, or leaping 

 or digging limbs. A peculiar use of the anterior 

 members, as seen in grasping the food and con- 

 veying it to the mouth (perhaps originally a 

 simple orifice witli soft lips, as in Peripatus), 

 would tend to cause such limbs to be grouped 

 together, to concentrate around the mouth-opening, and to be 

 directed constantly forwards. With use, as in tlie case of legs, 

 these originally soft mouth-feet would gradually harden at the 

 extremities, until serviceable in biting, when they would become 

 jaws and palpi. Given a mouth and limbs surrounding it, and 

 we at once have a rude head set off from the rest of the body. 

 And in fact such is the history of the development of these 

 parts in the embryo. At first the head is indicated by the buds 

 forming the rudiments of limbs; the 

 segments to which they are attached 

 do not form a true head until after 

 the mouth-parts have attained their 

 jaw-like cliaracters, and it is not un- 

 til the insect is about to be hatched, 

 that the head is definitely walled in. 

 We have arrived, then, at our Lep- 

 tus, with a head bearing two pairs 

 of jaws. The spiders and mites do 

 not advance beyond this stage. But 

 in the true insects and Myriopods, we have the addition of 

 special sense organs, the antenna;, and another pair of appen- 

 dages, the labial palpi. It is evident that in the ancestor of 

 these two groups the first pair of appendages became early 

 adapted for purely sensory purposes, and were natnrally pro- 

 jected far in advance of the mouth, forming the antennae. 



Before considering the changes from the mandibulate form 



203. Ephydra. 



