50 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



sp-- 



Muscular 

 System . 



were uniformly eight, two of which were situated on the inferior surface 

 of the spinneret at a greater distance from the extremity than the rest, 

 and were minute and ahnost contiguous. 



It is a fact deserving notice that the spinning spools are not always 

 developed simultaneously on these spinnerets, six, seven, and eight being 

 sometimes observed on one, while five, six, or seven are to be seen on the 

 other -This remark is applicable not to the anterior spinnerets alone, but 

 to the intermediate ones also, which, in mature individuals, are further 

 modified by having the extremities of the terminal joints directed forwards 

 at rioht angles to their bases. The same condition was observed m a 

 species of Drassus and in Segcstria senoculata. It is not improbable, there- 

 fore, that other species, and per- 

 haps all spiders, follow the same 

 law of development. 



This whole system of liquid 

 silk supply is regulated by the 

 compression of surround- 

 ing muscles, which act 

 upon the several glands 

 in the manner of the hand when 

 squeezing upon the rubber bulb of 

 a spraying tube. The contents are 

 forced out of the glands in this 

 liquid condition, through the long, 

 delicate ducts, into the hollow spin- 



Fui. 46. Epeira diademata. sp (p), spigot of treeform nillg tubcS, whcilCe they isSUC ill 

 gland on posterior spinneret; ss,^^ . • ^^ thrOUgh the Cxtcrior 



glands on same. (After UnderniU.) \ 165. J » 



openings or mouths of the spools. 

 As tlio points of the spools or tips of the spinnerets are approximated, a 

 number of tliese jets flow together, and hardening instantly upon contact 

 with the air, form the thread or line familiarly known as the spider's web. 



The excretory ducts, as well as the silk glands themselves, are encircled by 

 a fibrous or muscular coat, which loosely surrounds them, and seems to be a 

 continuation of the outer coat or sac itself. The spinnerets are connected 

 with, or surmount the integument of the abdomen, by means of diverging 

 bands of muscular fibres, which enable them to move in different directions. 

 These muscles are placed immediately beneath the skin, and their expanded 

 extremities are inserted into it so that they are separated with it, unless 

 dissected very carefully. ^ 



All the si)iiinerets are thus })rovided with many muscles which cause 

 the a])[)roachment of all the spools of one spinneret against one another, 

 as also the convergence of all the six s])innerets towards a central point, 

 id oidti' lo pioilucc in this way a single thread. For this })urposc the 



' MoiuU'. 



