268 CHAPTERS O.V EVOLUTION. 



stages of their development, and that they could have been developed 

 by having such a function." 



That this speculation is a highly probable one is proved by the 

 curious fact that one insect (Pteronarcys regalis) belonging to the 

 Orthoptera, inhabiting damp places, retains its gill-bearing organs 

 throughout life. The mere possibility of the aquatic origin of insects 

 is therefore placed beyond doubt by such an observation, whilst the 

 fact that Pteronarcys belongs to the ancient order Orthoptera, shows 

 its alliance with a primitive type of the insect class. 



The consideration of the probable original or type form of the insect 

 class now demands attention. The tyro in natural history knows that 

 insects, along with spiders and scorpions, centipedes and crustaceans, 

 form a great division of the animal world, to which the name of Arthro- 

 poda (" jointed-legged" animals) is given. The latter group in its turn 

 forms a division of the great Articulate type, of which group the 

 possession of a jointed body (seen equally well in the insect's body, 

 in the centipede's frame, or in the lobster's tail) is a chief characteristic. 

 Now, the origin of the Arthropoda from some lower and worm-like 

 stock is not a matter which involves any very great draught upon the 

 speculative faculty. From some such stock the tribes of spiders, 

 insects, crustaceans, and centipedes have probably originated. There 

 exists, indeed, a curious animal known as Peripattts, which is in many 

 respects entitled to be considered as a primitive Arthropod. From 

 some such form as Peripatus, it is not improbable that at least the 

 insects, centipedes, and spiders were evolved. We have discussed in 

 a previous chapter the nature of the form which has probably through 

 its evolution and development given origin to the crustacean hosts 

 and legions. This form is the Nauplius, which, in the development 

 of highest and lowest crustaceans alike, reappears as the root and 

 stock of the class, and whose modifications form the puzzles of the 

 philosophical naturalist of modern times. Now, what is so clear in 

 the case of the Crustacea is well-nigh as patent in the history of insects. 

 We certainly do possess in existing groups of insects forms which appear 

 to fulfil the conditions incidental to the purpose of serving as a gene- 

 ralised type from which insect evolution may have taken place. Such 

 groups are those known as the Thysanura, or " tuft-tailed " insects, 

 and the Collembola of Lubbock, both of which orders may be found 

 on examination to present us with the natural root stock of higher 

 insects. A brief inquiry into the characters of these latter insects 

 may appropriately bring this chapter to a close. 



Professor Huxley, in a recent manual of comparative anatomy, 

 speaks of the cockroach as an " insect without metamorphosis " a 

 fact already noticed and remarks upon the obvious difference which 

 exists between such a form as a butterfly, with its resting chrysalis, and 

 the young cockroach, active throughout its whole development. " It is 



