Tune, 1921.] CrAMPTOX : EVOLUTION OF THE AXTHROPODA. 03 



jections. It is a considerable leap from such a condition even to tlie 

 weakly developed type of mandible shown in tcxtfi,c:ure 3 (which is 

 infinitely more primitive than any insect's mandible), since in the 

 latter form, there is a small incisor ])rocess " c " distinct from the 

 molar process "/" (neither of which are present in the trilobite), 

 and the basal segrment of the limb has begun to take on a contour 

 suggestive of a mandilile — while the basal segment of the trilobite's 

 mandibular limb is just like the basal segment of its " walking " legs; 

 and the Icaj) from such a basal segment to one of the mandibular 

 type bearing not only an incisor process, but a lacinia mobilis. molar 

 process, and other complicated structures, such as occur in the man- 

 dibles of immature ephemcrids (whose mandi])les are the most 

 primitive of any winged insect thus far studied) involves such pro- 

 found and fundamental changes in structure, that if we had only the 

 evidence of the mandibles alone, to judge from, it would be im- 

 possible to justify Handlirsch's impossible claim that winged insects 

 (or even the far more primitive apterygotan insects) were derived 

 directly from trilobites; and it is indeed astounding that such revolu- 

 tionary claims have been so readily accepted by scientific men who 

 are usually more than " conservative " in accepting new views which 

 are not demonstrated by almost irrefutable facts! 



The nature of the mandiljular appendages, in addition to the evi- 

 dence drawn from many other sources, would indicate that the 

 ■■higher" Crustacea, {i.e., Amphipoda, Isopoda. Tanaidacea. etc.) 

 together with the Insecta and Symphylo-Pauropoda, were in all proba- 

 bility derived from common ancestors anatomically intermediate be- 

 tween the Mysidacea on the one side and the Syncarida on the other, 

 and these common ancestral types were probably also related to the 

 Arthropleura and Oxyuropoda as well. Starting from this common 

 source, the lines of descent of the Insecta were paralleled on one side 

 by the '■ higher " Crustacea, and on the other by the lines of descent 

 of the Symphylo-Pauropoda. The symphylan line of development 

 I)aralleled that of the Insecta only as far as the jioint where the 

 Dicellura (Campodca, J a pyx. etc.) were developed, whereupon the 

 lines of development of the Symphyla and the Dicellura appear to be- 

 come specialized in a direction which does not lead to the production 

 of types approaching the winged insects. On the other hand, the 



