2 7 



CHAPTERS ON EVOLUTION. 



Their popular name of " spring-tails," derived from the presence of 

 appendages formed on a "spring and catch" principle, and by means 

 of which they are enabled to take leaps of considerable extent, 

 indicates another peculiarity of the group. Only in one genus of 

 the Collembola, likewise, are breathing tubes found. The jaws or 

 "gnathites" in Campodea and the Collembola are not very markedly 

 developed. As Sir J. Lubbock remarks, the jaws "are far from 

 strong, but still fcave some freedom of motion, and can be used for 

 biting and chewing soft substances." Of these lower insects, the 

 genus Campodea (Fig. 181, B) is particularly interesting, inasmuch 

 as it seems to combine in its person all the primitive characters 

 which give to its neighbours their extreme interest in the eyes of 

 naturalists. Campodea, which occurs in loose damp earth, has an 

 elongated cylindrical body, long and many-jointed antennae, with 

 paired appendages on the first seven joints of its tail, and 

 long tail-appendages likewise. Now, if we compare the 

 young or larva of Campodea (Fig. 181, A) with the adult 

 (B), we find little or no difference save in size. Its whole 

 organisation reminds us forcibly of the young stage in such 

 insects as the cockroaches and other Orthoptera (Figs. 173, 

 176); whilst there are larvae in other groups of insects 

 to which Campodea and its neighbours bear a close re- 

 semblance. Furthermore, the larva (Fig. 171, A) of the 

 day-fly (Chloeori), which possesses the gill appendages 

 already referred to, is exceedingly like this Campodea, 

 whose mouth-parts appear equally capable of further deve- 

 lopment to form the jaws of the beetle, or of modification 

 to become the suctorial apparatus of the butterfly. 



Thus, on all the grounds on which it is possible or 

 necessary to look for resemblances between Campodea 

 and the young of higher insects, such likenesses are 

 discoverable. And the conclusion is thus rendered highly 

 probable that existing insects have been evolved from an 

 ancient Campodea-like stock that is, from an animal form 

 with a jointed body, three pairs of legs, weak mouth-parts, 

 one pair of feelers, and a tail provided with jointed ap- 

 ^moil 2 .' pendages. Hence a mental forecast is prepared to see 

 this Campodea-form developing in one direction, through 

 an insect like the young Chloeon (Fig. 171, A), or the water- larvae 

 (Fig. 1 79) already described, with their side " gills," into winged and 

 higher races. Or in another direction, and through less modification 

 perhaps, we may in our " mind's eye " behold Campodea growing 

 in time into the stock whence the Orthoptera our existing crickets 

 (Fig. 176), grasshoppers (Fig. 1 75), and locusts themselves a primitive 

 group of insects, have sprung. Backwards, on the other hand, 



