SPINNING GLANDS 



335 



Spinning Glands. — Spiders vary greatly in their spinning 

 powers. Some only use their silk for spinning a cocoon to pro- 

 tect their eggs, while others employ it to make snares and re- 

 treats, to bind up their prey, and to anchor themselves to spots to 

 which they may wish to return, and whence they "drag at each 

 remove a lengthening chain." 



All these functions are performed by the silk-glands of the Orb- 

 weavers, and hence it is with them that the organs have attained 

 their greatest perfection. We may conveniently take the case of 

 the common large Garden-spider, Upcira diademata. The glands 

 occupy the entire floor of the abdomen. They have been very 

 thoroughly investigated by Apstein,^ and may lie divided into 

 five kinds. 



On either side of the abdomen there are two large " ampul- 

 laceal " glands debouching on " spigots," one on the anterior, and 

 one on the middle spinneret ; there are three large " aggregate " 

 glands which all terminate on spigots on 

 the posterior spinneret ; and three " tubuli- 

 form " glands, two of which have their 

 orifices on the posterior, and one on the 

 middle spinneret. Thus, in the entire 

 abdomen there are sixteen large glands, 

 terminating in the large fusulae known as 

 spigots. In addition to this there are 

 about 200 " piriform " glands whose open- 

 ings are on the short conical fusulae of 

 the posterior and anterior spinnerets, and 

 about 400 " aciniform 

 debouch, by cylindrical fusulae, on the 

 middle and posterior spinnerets. Thus 

 there are, in all, about 600 glands with their separate fusulae 

 in the case of Epeira diademata. 



The great number of orifices from which silk may be emitted 

 has given rise to the widespread belief that, fine as the Spider's 

 line is, it is woven of hundreds of strands. This is an entire 

 misconception, as we shall liave occasion to show when we deal 

 with the various spinning operations. 



A few families are, as has already been stated, characterised 

 by the possession of an extra spinning organ, tlie cribellum, and 



1 Arch.f. Natunj. 55 Jahrg., i., 1889, p. 29. 



C 



glands which Fig. 187.— Spinning glands. 



A, Aciniform ; B, tubuli- 



foi'ui ; C, pirilorni glaud. 



