818 



CLASS V. ARACHNIDA. 



also well adapted for running 

 lightly on the threads. There are 

 a very great number and variety 

 of webs and snares built by spiders 

 which it is impossible to even 

 enumerate here, but mention must 

 be made of certain streamers of silk 

 which the young spiders, having 

 previously ascended to a rail-top 

 or some such place of vantage, let 

 out of their spinnerets ; the wind 

 catching these, as it might a para- 

 chute, wafts the spider into the air 

 and often carries it considerable 

 distances. These streamers form 

 the so-called gossamer, the origin 

 of which was for a long time a 

 mystery. 



The nervous system is very 

 concentrated ; there is a supra- 

 oesophageal ganglion supplying 

 the chelicerae and the eyes, and 

 a large star-like infra-oesophageal 

 mass supplying the rest of the 



appendages and the body (Fig. 537, 9, 10, Fig. 538). Between 



the two passes the minute oesophagus. 



The generative organs lie concealed amongst the branches of 



the " liver." The testes (Fig. 539) are two cylindrical organs 



opening into coiled vasa deferentia which 



unite to open by a single aperture at the 



anterior ventral end of the abdomen. 



The ovary is annular and the eggs pro- 

 ject from the surface of the gland (Fig. 



537, 13). Anteriorly the ovary passes into 



short oviducts which act as spermathecae ; 



they open separately and the opening may 



be protected and complicated by an " epi- 



.,, FIG 539. Sexual organs 



gyne. Spiders prepare either nests or of a Tegenaria domestica, 



. , , . j , i , , with the abdomen in out- 



cocoons for their young, and the latter are i me (after Bertkau). T 



. , . -i testis ; Vd vas deferens ; 



sometimes carried about lor a time by st > stigma. 



FIG. 538. Avicularia, ventral side, 

 part of the skin is turned aside. 

 K Chelicera ; Bg thoracic ganglionic 

 mass ; P, P' lungs ; F lamellae of 

 the lungs ; St, St' stigmata ; Ov 

 ovary ; Sw spinnerets. 



St 



