160 HINTS ON THE ANCESTRY OF INSECTS. 



for the transmutation of any worm with which we are at present 

 acquainted into a form like the Leptus, with its mandibuhited 

 moutli and jointed legs, seems at first well nigh impossible. 

 We have the faintest possible indication in the structure of 

 some mites, and of the Tardigrades and Peutastoma, where 

 there is a striking recurrence, as we may term it, to a worm-like 

 form, readily noticed by every observer, wiiatever his opinion 

 may be on the developmental theory. lu the Demodex we see 

 a tendency of the mite to assume under peculiar circumstances 

 an elongated, worm-like form. The mouth-parts are aborted 

 (though from what we know of the embryology of other mites, 



Ithey probably 

 are indicated 

 I early in embry- 

 onic life), wiiile 

 I the eight legs are 

 not jointed, and 

 form simple tu- 

 bercles. In the 

 Tardigrades, a 

 long step lower, 

 we have un- 

 jjointed fleshy 

 legs armed with 

 from two to four 

 claws, but the 

 month-parts are 

 essentially mite 

 I in character. A 

 191. Naupllus. decided worm 



feature is the fact that they are hermaphrodites, each individual 

 having ovaries and spermaries, as is the case with many worms. 

 When we come to the singular creatures of which Peutastoma 

 and Linguatula are the type, Ave have the most s>triking approx- 

 imation to the worms in external foi-m, but these are induced 

 evidently by their parasitic mode of life. They lose the rudi- 

 mentary jointed limbs which some (Linguatula especially) have 

 well marked in the embryo, and from being oval, rudely mite- 

 like in form, they elongate, and only the claws or simple curved 

 hooks, like those of young tape wotms, remain to indicate the 

 original presence of true jointed legs. 



