ORDERS OF INSECTS. 73 



meat, in cheese, in manure, in water, in mud, &c. They 

 pass through a complete metamorphosis. 



VII. Aptera. In this order is included a great variety of 

 insects that are destitute of wings. It is true that in the pre- 

 ceding orders are arranged many sorts of insects, which are 

 destitute of wings ; but they are so arranged, because, in their 

 general structure and habits of life, they resemble the other 

 members of the order. The Aptera, however, have no such 

 resemblance, and are therefore placed by themselves. Some 

 naturalists divide them into several orders, according to their 

 natural connections with one another ; but this is not necessary 

 here. Among them are found the millepedes, whose body is 

 divided into a great number of rings, each of which serves 

 for the attachment of one or more pairs of legs ; the louse, of 

 which there are many kinds which infest the bodies of men, 

 inferior animals, and plants ; thepuceron, &/c. Some of these 

 animals cover the surface of plants so completely, as to pro- 

 duce the appearance of a diseased change of structure. The 

 flea also belongs to this order, and is the only one that under- 

 goes any metamorphosis. It passes through the three stages. 

 Its power of leaping to a great distance is well known. 



The family of the Arachnides, or Spiders, is not always ar- 

 ranged among Insects, and strictly speaking, their structure 

 is different in some important particulars. We shall, however, 

 give some account of them in connection with the Aptera, 

 among which they were included by Linnaeus. This family 

 comprehends, besides the common spiders, the scorpion, the 

 tarantula, the crab-scorpion, the various species of mites, and 

 the animal which has been supposed to cause the Psora or 

 itch, by insinuating itself beneath the skin. 



They are distinguished from all other insects by the absence 

 of the antennae. A part of them breathe like insects by 

 means of trachea? distributed throughout their bodies ; while, 

 in the rest, the tracheae open into pulmonary sacks, which 

 answer the purpose of lungs. In the latter, there is found a 

 well-organized heart and a vascular circulation, which are 

 absent in the former. They have generally eight legs, and 

 are furnished with six or eight eyes, which enable them to 

 perceive objects in several different directions at once. They 

 are nourished generally by living prey, and are provided with 

 means for securing and destroying it. The Spider effects this 

 by means of the web that it spins, in the construction of which 

 much ingenuity is often manifested. The threads of which 

 "t is composed, are produced from six little fleshy bunches, 

 7 



