The External Anatomy of Spiders 



The spinning tubes.— - There are many small tubes distributed 

 over the surface of the spinning field ; these are the spinning tubes; 

 it is through them that the silk is expelled from the body. Usually 

 ach spinning tube consists of two segments, a stouter basal one and 

 a more slender terminal one (Fig. 138). Some spiders have one 

 hundred or more of these spinning tubes on each spinneret. The 

 number of spinning tubes varies greatly in different species, and 



c d. e . 



Fig. 138. THE SPINNING TUBES OF 

 ARANEA SEEN IN OPTICAL SECTION 

 a, of aciniform glands b, of pyriform 

 glands c , of ampullate glands </, of 

 cylindrical glands e, of aggre- 

 gate glands (after Apstein) 



Fig. 140. THE SPIXXERETS 



AND THE CRIBELLTJM OF 



AMAUROBIUS 



Fig. 13Q. HIND SPIXXERET OF STEA- 

 TODA SHOWING TWO SPIGOTS 

 WITHOUT A TIP (after Apstein) 



Fig. 141. THE CRIBELLUM 



(il AMAUROBIUS -MORE 



ENLARGED 



also in different individuals of the same species. It may be that the 

 number increases with age; but we lack observations on this point. 



Although the spinning tubes are almost invariably borne by 

 the tip of the spinneret, in a few cases there is one or more on 

 the basal segment of a two-jointed spinneret. 



There are four different types of spinning tubes: the long 

 and cylindrical (Fig. 138, a); the short and conical (Fig. 138, b); 

 a form much larger than the preceding, which is termed a spigot 

 (Fig. 138, c, d, e); and a spigot without a tip (Fig. 139). 



Different kinds of silk are spun from the different kinds of 

 spinning tubes. 



1 }5 



