SPINNING APPARATUS OF SPIBERS. 



583 



FlQ. 297. 



Foot, with comb-like claws, of the common Spider 

 (Epeira). 



Fia. 298, 



the last joint of the foot is furnished, have their edges cut into 

 comh-like teeth (Fig. 297), 

 which seem to be used by 

 the animal as cleansing 

 instruments. One of the 

 most curious parts of the 

 organization of the Spiders 

 is the* " spinning appara- 

 tus," by means of which 

 they fabricate their elabo- 

 rately constructed webs. 

 This consists of the " spin- 

 nerets," and of the glandu- 

 lar organs in which the 

 fluid that hardens into the 

 thread is elaborated. The 

 usual number of the spinnerets, which are situated at the poste- 

 rior extremity of the body, is six ; they are little teat-like promi- 

 nences, beset with hairy appendages ; and it is through a certain 

 set of these appendages, which are tubular and terminate in 

 fine-drawn points, that the glutinous secretion is forced out in a 

 multitude of streams of extreme minuteness. These streams 

 harden into fibrils, immediately on coming into contact with 

 the air; and the fibrils proceeding from all the 

 apertures of "each spinneret, coalesce into a single 

 thread. It is doubtful, however, whether all the 

 spinnerets are in action at once, or whether those 

 of different pairs may not have dissimilar functions; 

 for whilst the radiating threads of a spider's web 

 are simple (Fig. 298, a), those which lie across 

 these, forming its concentric circles or rather poly- 

 gons, are studded at intervals with viscid globules 

 (b), which appear to give to these threads their 

 peculiarly adhesive character ; and it does not seem 

 by any means unlikely, that each kind of thread 

 should be produced by its own pair of spinnerets. 

 The total number of spinning tubes varies greatly, 

 according to the species of the spider, and the sex 

 and age of the individual ; being more than 1000 

 in some cases, and less than 100 in others. The 

 size and complexity of the secreting glandulte vary 

 in like manner: thus in the Spiders which are most 

 remarkable for the large dimensions and regular 

 construction of their webs, they occupy a large 

 portion of the abdominal cavity, and are ^omposed 

 of slender branching tubes, whose length is in- 

 creased by numerous convolutions; whilst in those which have 

 only occasional use for their threads, the secreting organs are 

 either short and simple follicles, or are undivided tubes of mode- 

 rate length. 



a 



Ordinary thread 

 (a), and glmi- ' 

 nous thread (b), 

 of the uommon 

 Spider. 



