FOLSOM: MOUXn-PARTS OF AXUKIDA MAKITIMA. 149 



the ocular segment, every somite is represented h\ a pair of append- 

 ages. I find no evidence whatever fur more than seven primitive 

 cephalic segments, and believe that my observations have assisted 

 to settle the long-disputed question of the segmentation of the 

 head. 



Since the time of Fabricius, the mouth-parts of insects have been of 

 primary importance for the systematist. While insisting that a logical 

 classification must recognize all anatomical structures, it must be ad- 

 mitted that the mouth-parts are of fundamental systematic value on 

 account of the range of their differentiation. 



Without discussing at length the phylogeny of insects, I may briefly 

 give the bearing of these studies ujiou the subject, remarking that my 

 conclusions are in entire accord with approved views upon the origin 

 of insects. 



The Collembola are strikingly like Campodea and Japyx in structure, 

 their peculiar entognathous characteristic separating these three groups 

 from all other insects. The Collembola as a group are somewhat more 

 specialized than the Thysanura in general structure. The Smynthuridse, 

 with their globular bodies, vertical heads, and well-developed furculse 

 and ventral tubes, represent one extreme of differentiation — compara- 

 tively high. The Aphoruridse, including Anurida, with vermiform 

 bodies, subequal segments, horizontal heads, no furcula, etc., are much 

 more generalized, and probably degenerate forms. Anurida, for ex- 

 ample, has both pairs of maxillary palpi, as well as rudimentary ab- 

 dominal appendages and the fundaments of a furcula in the embryo, 

 but in the embryo only. Therefore the ancestral Collembolan was 

 probably intermediate between Smynthuridse and Aphoruridie, and is 

 most nearly represented by members of the family Poduridse. The 

 resemblance in the mouth-parts leads us to suppose that the primitive 

 Collembolan descended from the stem form of Campodea and not far 

 below Campodea itself. 



The affinities of Campodea, which is slightly more primitive than 

 Japyx, are in two directions : towards Machilis and Lepisma on the one 

 hand, and towards Scolopendrella on the other. In the first two genera 

 the mouth-parts are clearly derivable from the Campodean type, and 

 link Campodea with Orthoptera. In regard to Scolopendrella, it was 

 long uncertain whether it should be placed among Thysanura or 

 Myriopoda, on account of its strong aflBnities for both. Most authors 

 have followed Orassi and placed it in the latter group, always admitting 

 its msectean features. In the mouth-parts, Scolopendrella approaches 



VOL. XXXVI. — NO. 5 f) 



