ZOOLOGY. 



interlaced with remarkable art; and it has been calculate! 

 that ten thousand threads as they come from the pores of one 

 of the winders of some of our common spiders, do not equal 

 in thickness one of our hairs ; whilst other species, peculiar to 

 hot countries, form nets so strong that they suffice to arrest 

 tin- progress of small birds, and even man himself is obliged to 

 make an effort to break through them. The manner in 

 which spiders arrange their silk is no less varied: some 

 routine themselves to stretch irregular threads, and others 

 weave a web, the meshes of which are of extreme regularity. 

 Sometimes we see them immovable in the middle of their 

 web, watching their prey; at other times, they conceal 

 themselves in a retreat which they construct at hand, and 

 which sometimes has the appearance of a silky tube. > mu- 

 tinies that of a small cup or cupola. 



559. The arachnida are divided into two orders, accord- 

 ing to the structure of the organs of respiration and of 

 circulation. 



The arachnida pulmonaria are chiefly characterized by the 

 presence of pulmonary pouches and of a well developed vas- 

 cular apparatus ; but they may also be 

 recognised by other peculiarities of struc- 

 ture. Thus, their eyes are six. eight, 

 or even more in number, and under the 

 abdomen may be seen two, four, or 

 eight stigmata Moreover, the general 

 form of these animals varies. Some- 

 times they have the abdomen globular, 

 winders at its extremity, and small 

 mandibular feelers ; at other times the 

 abdomen is elongated, and composed 

 of several rings; their mandibular feel- 

 ers advance like arms, and terminate- 

 like forceps ; or finally, there exists no 

 winders at the extremity of the i>odv, 

 but in general a venomous apparatus. 

 Spiders, properly so called (Fig. 151), that is to say. the 

 inygale (Fig. 409), the cpeira, the lycosce or tarantula-, the 

 theridions (Fig. -11(5). present us with the first of these two 

 modes of conformation ; the scorpion (Fig. 413), the second. 



"' i. The arachnjda tracheari;e have no pulmonary 

 pouches, but respire by trachea?, like insects, and have 

 only a rudimentary vascular apparatus lor the circulation of 



Km. U6. Theridion 

 inalini^nathe. 



