STRUCTURE AND ECONOMY OF SPIDERS. 317 
lific eggs without sexual intercourse, nevertheless, 
when thus circumstanced, do occasionally produce 
eggs that are sterile. . 
Four, six, or eight mammule, somewhat conical or 
cylindrical in figure, and composed of one or more 
joints each, constitute the external spinning-appara- 
tus of the Araneidea : they are usually closely grouped 
in pairs at the extremity of the abdomen, and are 
readily distinguished from each other by their relative 
positions. The pair situated nearest to the anus may 
be denominated the superior spinners ; the pair fur- 
thest removed from the anus the inferior spinners ; 
and the mammule placed between these extremes 
the intermediate spinners, distinguishing them, when 
there are two pairs, by prefixing the terms superior 
and inferior. Exceedingly fine movable papille or 
spinning-tubes, for the most part dilated at the base, 
occur at the extremity of the mammule, or are dis- 
posed along the inferior surface of their terminal 
joint, whence issues the viscous secretion of which 
all the silken lines produced by spiders are formed. 
The. papilla connected with the mammule vary 
greatly in number in different species of spiders, and 
also differ considerably in size, not only in individuals 
of the same species, but often even on the same 
mammule. 
Among our native spiders, the larger species of 
Epeira have the mammule most amply provided with 
papillz ; it is certain, however, that the total number 
