ARTIOCULATA. 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 Arado 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 J?tilota of Aristotle 
(the winged insects) in one class, and the Ametabola in another, the latter 
being composed of the four orders, Chilognatha, Chilopoda, 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 Chilopoda (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. Various species in the United 
States are described by Say, in the Journal of the Academy of Natural 
Science, vol. ii., 1821. 
Orver 1. CuttocnatHa. The genus /ulus may be taken as the type of 
this order, in which the body is slender, composed of many segments of a 
crustaceous consistence externally, Air cylindrical, and Hee with a 
multitude of short feet arranged in double pairs, eee 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 antennee 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, Glomeride, Polyxenide, Polydes- 
mide, Iulide Polyzonide, and Siphonophoride. 
The body of Zudws 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 (Z. marginatus, Say), 
resembles muriatic acid. This species is three inches long, blackish, and 
the segments have a rufous margin. 
Onper 2. Cuitoropa. Here the body is depressed and linear, with a 
tough exterior, and the segments are proportionally longer, and not so 
numerous as in the eee The feet also are less numerous, and the 
posterior pair are usually projected backwards in the manner of a i and 
used in drawing the body backwards. The antenne are slender and 
tapering, and Bane! 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. 
