122 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



merited. Some of the Anthracomarti resemble the trilobites more closely than do the Aranere, 

 as they lack the constriction between the cephalothorax and abdomen. The spiders of the 

 Pennsylvanian have this constriction less perfectly developed than do modern Aranerc, and 

 occupy an intermediate position in this respect. In the Anthracomarti, the pedipalpi are 

 simple, pediform, and all the appendages have very much the appearance of the coxopodites 

 and endopodites of trilobites. Chelicerse are not known, and pleural lobes are well devel- 

 oped in this group. Anthracomarti have not yet been found in strata older than the Penn- 

 sylvanian, but they seem to be to a certain extent intermediate between true spiders and the 

 marine arachnid. 



INSECTA. 



Handlirsch (in several papers, most of which are collected in "Die Fossilen Insekten," 

 1908) has attempted to show that all the Arthropoda can be derived from the Trilobita, 

 and has advocated the view that the Insecta sprang directly from that group, without the 

 intervention of other tracheate stock. At first sight, this transformation seems almost 

 an impossibility, and the view does not seem to have gained any great headway among ento- 

 mologists in the fourteen years since it was first promulgated. If an adult trilobite be com- 

 pared with an adult modern insect, few likenesses will be seen, but when the trilobite is 

 stripped of its specializations and compared with the germ-band of a primitive insect, the 

 theory begins to seem more possible. 



Handlirsch really presented very little specific evidence in favor of his theory. In fact, 

 one gets the impression that he has insisted on only two points. Firstly, that the most 

 ancient known insects, the Palaeodictyoptera, were amphibious, and their larvae, which lived 

 in water, were very like the adult. Secondly, that the wings of the Palasodictyoptera prob- 

 ably worked vertically only, and the two main wings were homologous with rudimentary 

 wing-like outgrowths on each segment of the body. These outgrowths have the appear- 

 ance of, and might have been derived from, the pleural lobes of trilobites. 



He figured (1908, p. 1305, fig. 7) a reconstructed larva of a palaeodictyopterid as 

 having biramous limbs on each segment, but so far as I can find, this figure is purely schematic, 

 for there seems to be no illustration or description of any such larva in the body of his work. 



That the insects arose directly from aquatic animals is of course possible, and Hand- 

 lirsch's first argument has considerable force. It may, however, be purely a chance that the 

 oldest insects now known to us happen to be an amphibious tribe. The Palacodictyoptera 

 are not yet known to antedate the Pennsylvanian, but there can be no doubt that, insects 

 existed long before that time, and the fact that their remains have not been found is good 

 evidence that the pre-Pennsylvanian insects were not aquatic. Comstock, who has recently 

 investigated the matter, does not believe that the Palaeodictyoptera were amphibious (The 

 Wings of Insects, Ithaca, N. Y., 1918, p. 91). 



The second argument, that wings arose from the pleural lobes of trilobites, is exceedingly 

 weak. Where most fully set forth (1907, p. 157), he suggests that trilobites may occasion- 

 ally have left the water, climbed a steep bank or a plant, and then glided back into their native 

 element, taking advantage of the broad flat shape to make a comfortable and gentle descent ! 

 This sport apparently became so engaging that the animal tried experiments with flexible 

 wing tips, eventually got the whole of the pleural lobes in a flexible condition, and selected 

 those of the second and third thoracic segments for preservation, while discarding the 

 remainder. The pleural lobes of trilobites are not only too firmly joined to the axial portion 



