504 Prof. J. D. Dana on the 



The abdomen of tlie Eurypterid, however, exists a3 a slender- 

 jointed thread in Geralinura of Scudder, of tlie Carboniferous, 

 whicli has its Illinois and also Bohemian species, and has 

 survived till now in the modern Telyphonus. 



Derivation of Myriapods and Insects. — Myriapods, although 

 inferior to Insects, are as yet known only from the early 

 Devonian. The Devonian species, and also those of the 

 Carboniferous, are of the Millepede or lower doubly multi- 

 plicate section of Myriajiods, with one exception, that of the 

 remarkable fcw-jointcd caterj)illar-like PaUeocampa of ^Icek 

 and Worthen. 



The fact of a line of succession from Worms to ilyriapods 

 and from Myriapods to Insects has not been proved by ideolo- 

 gical discovery. The derivation of ]\lyriapods from some 

 type of Annelids is zoologically suggested, as long since 

 recognized, by the apparently transitional form of Feripatas^ 

 a low-grade Myriapod resembling much the larva of some 

 Insects, and by the like multiplicate structure of Annelids 

 and Myriapods. It might be inferred also from the resem- 

 blance of the Palceocampa of the Illinois Carboniferous to the 

 caterpillar of an Insect of the genus Aixtia, as remarked by 

 Scudder. 



Myriapods are regarded as the precursors of Insects on 

 account of their approximate resemblance to the latter in 

 antennae and the api)endages of the mouth, and because also 

 of the worm-like form of most Insect larvae, these larvaj 

 appearing to be survivals of the Myriapod stage. In the 

 change from an Annelid and Myriapod to an Insect the 

 vndtiplicate feature disappeared and the number of parts 

 became essentially the fixed normal number of the type, both 

 as regards the body-segments and their jointed appendages. 



The rise of grade from the ^Myriapod to the Insect involved 

 the ap})ropriation of the three body-segments of the Myriapod 

 bearing the three anterior pairs of feet (which correspond 

 normally to half tlie body-segments of the head of an Isopod 

 Crustacean) for forming the isolated middle section of the 

 body, called the thorax, and the suppression of all the other 

 pairs of feet. In both JSpiders and Insects the change involved 

 also a general concentration of the structure toward the 

 cej)halic nervous centre, that is a shortening of the range of 

 cephalic control, and especially the distance to the posterior 

 limit of locomotive action. Compared with a crab, the 

 highest type in the Crustacean series, its superior, an ant, is a 

 very little thing. 



The fact that in low-grade Insects there is no proper 

 mt'famorphosis^ while in the higher, as ihey rise in grade, rhe 



