INTRODUCTION. 
LiNNiEUS and the naturalists of his school have included spiders in the extensive class 
Insecta, having constituted with them the genus Aranea , comprised in the order Apteru. 
Subsequently, zoologists have removed the Aranece and several nearly allied groups from the 
apterous insects, and have established with them the class Araclmida. Of this class the 
spiders form the order Araneidea, which is divided into tribes, families, and genera. A concise 
summary of the more important facts relating to the organization and economy of these 
animals, which have been disclosed by the researches of anatomists and physiologists, will 
serve to elucidate the history of species. 
Spiders, with few exceptions, have a cephalo-thorax, or the head continuous with the 
chest; but the cephalic may readily be distinguished from the thoracic portion by the presence 
of the eyes, which are two, six, or eight in number; by the falces, 1 situated in front, and 
terminated by a pointed fang which has a ginglymoid movement; and by the oral apparatus 
connected with its inferior surface. The parts of the mouth consist of two maxillse, each 
provided with a palpus of five joints, having between them a sternal labium, and above them 
a palate to whose superior surface a small labrum is attached. Eight legs, of seven joipts 
each, having two or more claws at their extremity, are articulated round the cephalo-thorax, 
to the posterior part of which the abdomen is united by a short, cartilaginous pedicle. The 
abdomen is moveable, without division, terminated by a small, angular process, which covers 
the anal orifice, and by four, six, or eight fleshy mammulse, placed directly below the anus, 
from which the silk proceeds in the act of spinning. On the under side of the abdomen, near 
its anterior extremity, there are two or four respiratory apertures or stigmata; and in the 
middle of the space which separates them the external foramen of the sexual organs is situated 
in the females, but in the males these organs are connected with the terminal joint of the 
palpi; consequently, they are double. 
The cephalo-thorax is covered on the upper part with a plate, which is generally 
coriaceous, but in some instances is hard and corneous. It varies considerably in figure, the 
1 The term falces is applied to the organs improperly denominated mandibles, -which, being 
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situated above the labrum, form no part of the oral apparatus. See the ‘ Transactions of the Linnean 
Society,’ vol. xxi, p. 37. 
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