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SCIENCE. 



[N. S. Vol. V. No. 122. 



spur, very close, however, to the point from 

 "Which the roaches originated. The Der- 

 moptera cannot remain associated with the 

 Orthoptera and present more affinities to the 

 Coleoptera from my point of view. I do not 

 mean to say that the Earwigs were the an- 

 cestors of the beetles ; but that both were 

 derived from the same spur in which the 

 secondaries became transversely folded, and 

 the Dermoptera now present some of the es- 

 sential characters of the ancestral Coleop- 

 teron. The Coleoptera proved a vigorous 

 shoot and stand far the highest of all those 

 series with a freely movable or separate 

 prothorax. 



While the terrestrial branches were de- 

 veloping independently, two aquatic types, 

 the Plecoptera and Platyptera, became devel- 

 oped, the larval forms living similarly under 

 the surface of the water, but assuming a 

 winged, aerial type before becoming ca- 

 pable of reproducing their kind. The 

 Plecoptera or Stone-flies have the metamor- 

 phosis incomplete, while the Platyptera have 

 it complete. The differences in this respect 

 are very slight, however, and I have no 

 hesitation in classing these forms together 

 as comparatively small divergences from 

 one stem. It will be noted that I use the 

 term Platyptera in a different sense from 

 any in which it has been heretofore em- 

 ployed, and do not include with it either 

 the Chrysopidce, Hemerohiidce or Myrmele- 

 onidoe. Raphidia and Mantispa, which 

 seemed at first sight referable to this series 

 on account of the elongate prothorax, do 

 not really belong here, because this segment 

 is not free, but is closely united at its base 

 with the mesothorax. The Plecoptera are, 

 of course, much the most primitive and are 

 a survival, the main line of development 

 continuing in the direction of the Platyptera. 



The second branch from the Thysanuran 

 stem started with all the thoracic segments 

 nearly equally developed. "While the pro- 

 thorax was of good size and in the lowest 



forms quite free, yet the tendency was from 

 the very start ±o unite it at its base to the 

 other thoracic segments. In this series it 

 is always fairly well developed, sometimes 

 even very long; but it is always closely 

 joined to the meso-thorax at the base and is 

 not movable, while the tendency is for the 

 head to become free from it, and at all 

 events not to be inserted into the thoracic 

 segment. While we do not have anywhere 

 in this series a distinct neck, yet on the 

 other hand there is nowhere a retraction 

 of the head into the prothorax. In this 

 series both pairs of wings are similarly de- 

 veloped, both as to size and as to general 

 character, while the secondaries, though 

 frequently covered by the primaries, are 

 never folded beneath them in any way. 

 The primaries are always functional. 



The lowest in this series, and almost the 

 simplest in general structure, are the Isop- 

 tera, where all the thoracic segments are 

 well developed and the prothorax is scarcely 

 dominant, though larger and almost free 

 from the others. The wings are very much 

 alike, the secondaries only a little larger 

 than the primaries, and both are laid flat 

 upon the abdomen. The mouth structures 

 are almost identical with those of the ear- 

 wigs and some of the Orthoptei-a. I believe 

 the members of this order are among the 

 most primitive of all the terrestrial winged 

 insects now existing, and among the most 

 ancient, though remarkably specialized in 

 certain directions at the present time. 

 Though at first glance it would seem as if 

 these insects should belong to the series in 

 which the prothorax is free, yet the char- 

 acter of the wing structure forbids this asso- 

 ciation and makes the Igoptera a natural 

 stem from which were derived the Malloph- 

 aga, Corrodentia and Neuroptera. 



The Mallophaga are a degraded parasitic 

 type which were not improbably developed 

 from a wingless Isopteron, and perhaps at 

 about the time that the wingless forms of 



