//. ACERATA: ACARINA. 453 



hinder pair are replaced by tracheae, which may open by separate spiracles 

 (Tetrasticta) or by a common opening (Tristicta, fig. 460). 



Sub Order I. TETRAPNEUMONES. Four lungs, four spinnents and 

 eight eyes in two rows. The MYGALnxsare the most important group, large- 

 forms which spring upon their prey, capturing even small birds and mice. 

 To the genus Mygale* belong the spiders (commonly but erroneously called 

 tarantulas) which occur in banana bunches. Here also belong the trap- 

 door spiders, Cteniza,* of the southwest, which excavate burrows in the 



FIG. 471. Cteniza ccementaria in its tube, closing the lid. o, eyes ; b, inside of lid! 

 with places for the claws ; c, egg cocoon. 



soil, line them with silk, and close them with a hinged lid (fig. 471). 

 Atypus.* 



Sub Order II. DIPNEUMONES. One pair of lungs, one of trachea; 

 six spinnerets. Here belong most of the native and numerous tropical 

 species. Some (VAGABUND^E) use their webs only to line the nests and 

 enclose the eggs, which are either hidden away or carried about attached to 

 the body, while they spring upon or chase their prey. SEDENTARIA are- 

 the web builders, their webs varying widely in structure. Of the first 

 group the SALTIGRADA include forms which jump upon their prey (Attus,* 

 PhidippuS)* Habrocentrum*), and the CITIGRADA (Lycosa,* Dolomedes,* 

 Trochosa *), which run their prey down. Among these is the true Taran- 

 tula, T. apulice of Italy, whose bite was once believed to cause a frenzy only 

 to be cured by peculiar music (' Tarantello '). The Sedentaria are divided, 

 according to the web-building habits- The ORBITELARLE or orb weavers 

 (Epeira* Argiope*) form vertical webs which in many instances are com- 

 plete circles. The RETITELARLE (Theridium* Erigone *) build irregular 

 webs. The species of Latrodectes * are reputed poisonous to man (fig. 

 468). The TUBITELARI.E build horizontal webs with a tube to the mar- 

 gin in which they lay in wait for insects. 



Order II. Acarina. 



The mites, partly from parasitism, partly from other conditions 

 of life, have become, in some instances, considerably modified. 

 With the fusion of cephalothorax and abdomen the last traces of 

 segmentation in the body are lost. Yet they retain the six pairs 

 of appendages four pairs of legs which at once distinguish them 

 from the parasitic hexapods; and two pairs of mouth parts, modi- 

 fied into a sucking beak. This consists of a tube formed by the 



