ARTICULATA. 13] 



habits ; and although the number of feet is fourteen in Oniscus, and thirty- 

 two in the male and thirty-four in the female of Glomeris, the external resem- 

 blance is so striking, that Glomeris marginatus has often been taken for a 

 variety of Ar^madillo vulgaris. They have also been considered to be 

 Arachnida, and more generally, a subdivision of the true insects. West- 

 wood, following Macleay to a certain extent, places the Ptilota of Aristotle 

 (the winged insects) in one class, and the Ametahola in another, the latter 

 being composed of the four orders, ChilognatJia^ Chilojjoda^ Thysanura., 

 and Anoplura. The two first of these constitute the Myriapoda, and the 

 last includes the lice. These heterogeneous materials are thrown together 

 on account of their imperfect metamorphosis, a character which is indicated 

 in the name Ametabola. 



The class contains the two orders, Chilognatha (lip formed from the 

 jaws), and Chilojpoda (lip formed from feet), of which the former contains 

 twenty-one and the latter sixteen genera, in the classification of Newport 

 published in the Philosophical Transactions. Yarious species in the United 

 States are described by Say, in the Journal of the Academy of Natural 

 Science, vol. ii., 1821. 



Okdee 1. Chilognatha. The genus Ixdus may be taken as the type of 

 this order, in which the body is slender, composed of many segments of a 

 crustaceous consistence externally, often cylindrical, and provided with a 

 multitude of short feet arranged in double pairs, except anteriorly, where 

 they are single. The motion of these animals is slow, and when disturbed 

 they generally roll themselves into a ball or spiral. The antennje are short 

 and slender, two in number, and have seven articulations. The mandibles 

 are crustaceous, triarticulate, and without palpi ; the generative organs are 

 situated behind the seventh pair of feet in the male, and behind the second 

 pair in the female. The spiracles are situated behind each pair of feet, 

 and must not be confounded with the lateral outlets of the odoriferous 

 glands. 



The order contains the six families, Glomeridm, Polyxenidce^ Polydes- 

 ?mda?, lulidce Polyzonidce, and SijyJionojjJioridcc. 



The body of lulus is cylindrical, and composed of forty or more segments. 

 The genus is common, and widely distributed in various parts of the earth. 

 When disturbed, some of the species exude a disagreeable scent, which in 

 the large and common species of the United States {I. marginatus, Say), 

 resembles muriatic acid. This species is three inches long, blackish, and 

 the segments have a rufous margin. 



Order 2. Chilopoda. Here the body is depressed and linear, with a 

 tough exterior, and the segments are proportionally longer, and not so 

 numerous as in the Chilognatha. Tlie feet also are less numerous, and the 

 l)osterior pair are usually projected backwards in the manner of a tail, and 

 used in drawing the body backwards. The antennte are slender and 

 tapering, and composed of fourteen or more articulations. The mouth is 

 armed with a strong pair of curved jaws with a palpiform appendage. The 

 eyes are usually simple, four or five on each side, or absent. These animals 

 are nocturnal ; they live upon animal food, and run rapidly. 



335 



