CLASS AEACHNIDA: ORDEB AKANEiB. 



327 



to the animals upon which they feed.* At the posterior 

 extremity there are four to six projections, spinnerets, pierced 

 oftentimes with a thousand holes, through which flow httle 

 streams of gluey matter, that harden on exposure to the air, 

 and uniting, form a single thread, f Some species emit the 

 threads freely into the air, till their buoyancy will sustain 

 them in a balloon-flight, or, the ends adhering to some dis- 

 tant object, a bridge is formed by which they can pass over 

 streams and ditches. 



Mg. S88. 



"ft -» 



-- ' -■''^. 



Epmra diadima. Geometrical Spider. 



Araneidse. — The Geometrical Spider is so called from the 

 regularity of the radiating and circular lines of its web. 

 Mygalidae. — The Mason Spider constructs a subterranean 



* This is injurious to nian only when the system is predisposed to erysipelas, etc., 

 even a mosquito hite then being poisonous. 



+ The union of the threads is effected by a skillful manipulation of the hind feet, 

 the comb-like structure of the claws being peculiarly adapted for this purpose. The 

 silk of some genera is produced in great quantity. Thus Dr. B. G. Wilder wound 

 eeyeral miles of threads from the spinnerets of the NephVa plumipes found near 

 Charleston. See Sarper's Magazine, vol. xxxiv, p. 4S0 ; also yol. xxii, p. 323. 



