1204 MANUAL OF ZOOLOGY* 



amalgamation of the head and thorax into a single mass, which 

 is clearly separated from the abdomen by a slight constriction, 

 as well as by the fact that the maxillary palpi terminate in 

 movable claws, instead of chelas. Further, the extremity of 

 the abdomen is not furnished with a terminal hook, or ' sting.' 



ORDER II. ARANEIDA, or DIMEROSOMATA. -This order includes 

 the true Spiders, which are characterised by the amalgamation 

 of the cephalic and thoracic segments into a single mass, and 

 by the generally soft, unsegmented abdomen, attached to the 

 cephalothorax by a constricted portion, or peduncle. Respi- 

 ration is effected by pulmonary sacs usually in combination 

 with tracheee. (Hence the name Pulmotrachearia, sometimes 

 applied to the order.) The number of the pulmonary sacs is 

 smaller in the true Spiders than in the Scorpions, being either 

 two or four, opening by as many stigmata upon the under sur- 

 face of the abdomen. 



The head bears from six to eight simple eyes ; the mandibles 

 are simply hooked, and are perforated by the duct of a gland 

 which secretes a poisonous fluid; and the maxillary palpi are 

 never chelate. 



Spiders (fig. 59) are all predaceous animals, and many of 

 them possess the power of constructing webs for the capture 

 of their prey or for lining their abodes. For the production of 

 the web, Spiders are furnished with a special gland situated at 

 the extremity of the abdomen. The secretion of this gland is 

 a viscid fluid which hardens rapidly on exposure to air, and 

 which is cast into its proper, thread-like shape, by being passed 

 through what are called the ' spinnerets.' These are little 

 conical or cylindrical organs four or six in number, situated 

 below the extremity of the abdomen. The excretory ducts of 

 the gland open into the spinnerets, each of which has its 

 apex perforated by a great number of minute tubes, through 

 which the secretion of the gland has to pass before reaching 

 the air. Many spiders, however, do not construct any web, 

 unless it be for their own habitations, but hunt their prey for 

 themselves. 



As regards the reproductive process in the Spiders, it 

 appears certain that the act of copulation, so to speak, is per- 

 formed by the males by means of the maxillary palpi, the 

 extremities of which are specially modified for this purpose. 

 The tesfces are abdominal, but the semen appears to be stored 

 up in the enlarged extremities of the maxillary palps, which 

 thus perform the part of the vesiculae seminales. ' The most 

 careful observations, repeated by the most attentive and expe- 

 rienced entomologists, have led to the conviction that the ova 

 are fertilised by the alternate introduction into the vulva of 



