CLASS ARACHNIDA: ORDER ARAKE^:. 227 



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 little 

 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. 



Epelra diadlma, Geometrical Spider. 



Araneidae. The Geometrical Spider is so called from the 

 regularity of the radiating and circular lines of its web. 

 Mygalidse The Mason Spider constructs a subterranean 



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

 even a mosquito bite then being poisonous. 



t 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. Q. Wilder wound 

 several miles of threads from the spinnerets of the NepKila plumlpes found near 

 Charleston. See Harper's Magazine, vol. xxxiv, p. 450 ; also vol. xxii, p. 323. 



