Page:Wood 1865 - The Myriapoda of North America.djvu/109

244 again there is a similar but less marked degradation in value as we go from the higher to the lower order. There is very little alteration in the segments of the body in the Chilopoda. They are all formed after one common type; more or less parallelopipedal, with a solid sternum below and scutum above separated by membranous sides, which give origin to the appendages. The only important aberrations from this are the occasional fusion of two scuta into one, and at times a slight development of the atrophied subsegment. Not so in the Chilognatha; here there are three distinct types of form and composition of the segments. Now each of these is peculiar to one of the three divisions indicated, strongly corroborating their claims to rank as suborders.

There is one imperfection in my knowledge of the subject which I recognize and would guard against. I have never seen any of the species of the Polyxenidae, and have not read a sufficiently accurate description of them and their anatomy to be able to assign their place; yet is it questionable but that they belong in one of the three suborders? There seems to be no room for a fourth division.

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Caput segmentis duobus distinctis compositum. Corporis segmenta subsegmenta unica efformata, singula pedum par unicum instructa. Organorum sexualium apertura ad extremitatem posteriorem.

, Leach, Linn. Trans., vol. xi, 1815, p. 381.

, Latreille, Cours D'Entomologie, 1831, p. 175, et auctores.