3194 



THE JOINTED ANIMALS 



jointed pair, a similar posterior pair, and an intermediate single-jointed pair. 

 Between those of the front pair there is either a ftmctionless membranous piece, 

 the colulus, or a paired plate, the cribellum, which is studded with the apertures of 

 spinning glands. The eyes are occasionally arranged in three clusters, two being 

 in the middle and three close together on each side; but usually the three lateral 

 ones are scattered, and the eight eyes placed on the front of the head in two rows. 

 The Arachnomorphce are divided according to their structural characteristics and 

 web-making instincts into a number of tribes each containing one or more families. 

 The first tribe, Umbellitelarice, contains the single family Hypockilidcz, represented 

 by the genus Hypochilus in North America and Ectatostida in China. These two 

 spiders differ from all the rest in having the hinder pair of breathing organs in the 

 form of lung sacs; the cribellum and calamistrum being present and the long and 

 slender legs furnished with three claws. In the genus Hypochilus, which is found 

 in the forests of Tennessee, the web is constructed beneath overhanging rocks and 

 cliffs and has somewhat the form of an inverted saucer, made of thick white silk 







HOUSE SPIDERS. 

 a. Male ; b. Female (natural size) ; arrangement of eyes shown on left hand of figure. 



and kept in place by a loose network of threads. Beneath this web the spider 

 remains upside down, and it has the habit, common to other species, of violently 

 shaking the web when alarmed. In the tribe Pseudoterritelarice, as in the rest of 

 the section, the breathing organs of the hinder pair are in the form of tubular 

 tracheae, but their apertures are widely separated and situated immediately behind 

 those of the front pair. There is no cribellum nor calamistrum, and the eyes are 

 reduced in number, being usually six, but sometimes, as in Nops, only two. Two 

 well-known European representatives of this tribe constitute the genera Dysdera 

 and Segestria. The former, found not uncommonly under stones in damp places, 

 may be recognized by the coral-red color of its carapace, its bright yellow legs and 

 pale gray abdomen. It makes no snare, merely constructing a small silken case, 

 which serves as a protection to the mother and her eggs at the breeding season. 

 Segestria, on the contrary, is much darker colored, with a band of diamond-shaped 

 spots upon the upper side of the abdomen. It spins in holes in old walls a tubular 

 nest, from whose aperture threads which serve to intercept prey pass to surrounding 



