374 J. D. Tothill — The Ancestry of Insects. 



in 1885 it was revised and amplified into a form that lias been 

 in general use ever since. Packard in 1803 and 1870 suggested 

 a derivation through the Apterygogenea (Lepisma) from the 

 Myriopods. 



lvingsley in 1894 emphasized the close relationship between 

 insects and Chilopods and also the unnaturalness of the old 

 group "Tracheata." In 1903 Carpenter reviewed the whole 

 situation and came to the conclusion that Insects, Chilopods 

 and Diplopods were probably derived independently from 

 Symphyloid stock — a position that in the light of recent data 

 is open to several serious objections. 



Each of the various systems proposed has resulted from dis- 

 coveries in morphology, development, or in paleontology. In 

 recent years discoveries have been made in two directions, each 

 throwing light on the problem of insect genesis. Through the 

 efforts of Barrande, Walcott, Lindstrom, Beecher, and Ray- 

 mond, our knowledge of detailed structures and of develop- 

 ment in the interesting extinct group Trilobita has been 

 greatly extended. On the other hand, Handlirsch following 

 the trail blazed by Brongniart and Scudder has greatly enriched 

 our knowledge of insect paleontology. In his remarkable 

 book " Die Fossilen Insekten " there is proposed a new system 

 of classification based, as was Brauer's, on development, mor- 

 phology, and particularly on paleontology. There is also pro- 

 posed a heterodox ancestry in which the Hexapods are derived 

 not in the usual way through the Apterygogenea from terres- 

 trial tracheate myriopod-like animals but directly from trilo- 

 bites. This derivation is accepted without reserve hy Schuchert 

 (1915) in his exceedingly illuminating Text Book of Geology, 

 and it has also been accepted by Ruedemann (1916). While it 

 is suggestive and very helpful it is open to certain objections 

 and the time seems, therefore, opportune to once more review 

 the whole question of insect genesis. The object of the paper 

 will be largely achieved if it succeeds only in stimulating the 

 search for further facts. 



An examination of the available data. 



In tracing the lineage of any complex of related organisms 

 the first point is of course to discover the most generalized 

 members of the group. In the insects these have been sought 

 in both the wingless Apterygogenea and in the winged Ptery- 

 gogenea. In the case of the former it will serve the present 

 purpose to recall some of the salient features in a few charac- 

 teristic examples. In Lepisma saccharina (fig. 1, A and B), 

 the mouthparts are greatly specialized by reduction, the eyes 

 are also reduced; on the other hand the primitive number of 



