335 



Chapter XVIII. 

 Structure of Spiders. 



Modern naturalists do not rank spiders among in- 

 sects, because they have no antennae, and no division 

 between the head and the shoulders ; they breathe 

 by leaf-shaped gills, situated under the belly, instead 

 of spiracles in the sides ; have a heart connected 

 with these ; have eight legs instead of six ; and 

 eight fixed eyes. But as spiders are popularly con- 

 sidered insects, it will sufficiently suit our purpose to 

 introduce them here as such. 



The apparatus by which spiders construct their 

 ingenious fabrics is much more complicated than 

 that which we have described as common to the 

 various species of caterpillars. Caterpillars have 

 only two reservoirs for the materials of their silk ; 

 but spiders, according to the dissections of M. Trevi- 

 ranus, have four principal vessels, two larger and 

 two smaller, with a number of minute ones at their 

 base. Several small tubes branch towards the reser- 

 voirs, for carrying to them, no doubt, a supply of 

 the secreted material. Swammerdam describes them 

 as twisted into many coils of an agate colour.* We 

 do not find them coiled, but nearly straight, and of a 

 deep yellow colour. From these, when broken, threads 

 can be drawn out like those spun by the spider, 

 though we cannot draw them so fine by many degrees. 



From these little flasks or bags of gum, situated 

 near the anus, and not at the mouth as in cater- 

 pillars, a tube originates, and terminates in the exter 

 t Hill's Swammerdam, part i. p. 23. 



