TETKAl'NLL.MOXES. 641* 



body, thereby tightening tlie web in every direction so that the 

 vibration is prevented. 



" The construction of nets for catching food is not the only 

 use of the thread made by these spiders. Tliey seldom move 

 from place to phice without spinning a line after them as they 

 go. They are able by its use to drop safely from any height, 

 and when suspended by it are carried by the wind across wide 

 spaces without any exertion on their part, except to let out the 

 thread. The crevices in which they pass the winter and th", 

 leisure hours of summer, are partly lined and enclosed by a 

 coating of silk resembling that used for confining captin-ed in- 

 sects. The eggs are enclosed in a cocoon of the same mate- 

 rial, and there the young remain until they are strijug enough 

 to shift for themselves, growing to nearly donbU' their size 

 without apparent nourishment. 



"Several hundred young are produced by a single female, 

 but probably it is seldom that one-tenth of this number ever 

 reach adult size. Nearl}^ all the spiders which w^e see in webs 

 are females or young. They spend most of their time in the 

 vicinity of their webs, and many doubtless pass their lives 

 within a few yards of the place of their birth. The adult mules 

 are seldom seen building or occupying webs : they remain con- 

 cealed during the day, and at night wander about from web to 

 web. When 3'Oung there is no obvious difference between the 

 sexes, but as the time for the last moult ap[)roaches, the ends 

 of the palpi of the male swell to several times their former 

 size. When the time for the final moult arrives, both sexes 

 retire to their holes and cast off the skins of their entire bodies, 

 even to the claws. This process obliges them to remain con- 

 cealed until the new skin has acquired suffieient strength and 

 firmness, when they again return to their webs. The females 

 still resemble the 3'oung, except in size, but the males are 

 distinguished from them by the greater length of their limbs, 

 the diminished size of the posterior half of the body, and the 

 large and comi)licated joints of the palpi (Phite 12, fig. 8)." 



Tetrapneumones Latreille. The large hairy species of 

 Mygale differ from other si)ideis in having four lung-sacs and 

 as many stigmata, and onl3^ two pairs of spinnerets, of which 



