560 CLASS IX. 



of the intestinal canal there are in addition four small blind appen- 

 dages on each side 1 . In the spiders (Aranea L.) the oesophagus is 

 narrow, horny, bent first downwards, then upwards, and terminates 

 in a part which proceeds backwards, and can be dilated by muscles 

 attached to it 2 . This part becomes at its extremity more membra- 

 nous, and passes into the intestinal canal, which sends two lateral 

 arms forwards that bend themselves round in the cephalothorax 

 and approach each other or unite so as to form an annular stomach. 

 From this ring blind eversions proceed towards the feet, bend 

 downwards, and communicate with each other. From the same 

 point where the two lateral arms arise a middle canal exists, which 

 runs towards the abdomen and is gradually dilated in some degree. 

 The widened part receives on each side two large canals which 

 branch through the adipose body ; the intestinal canal then narrower 

 curves upwards and afterwards proceeds downwards, where, pre- 

 vious to its termination, an oval coecum is situated laterally. 



Organs of different form for the secretion of saliva are observed 

 in most genera of this class, and probably are wanting in none of 

 the arachnids, although their opening into the intestinal canal hasi 

 not been detected in all. In the Scorpions, where MECKEL S de- 

 nied altogether the existence of salivary organs, two longitudinal 

 sacs placed in the fore part of the abdominal cavity, their tortuous 

 canals running forwards in the cephalothorax, probably serve for 

 the secretion of saliva 4 . From the secretion of saliva the poison 

 should be distinguished, with which different species kill their prey 

 previous to devouring it. In the spiders there is situated at the 

 base of each of the mandibles, or sometimes in the mandibles them- 

 selves, a vesicle, surrounded by a layer of flat spirally turned fila- 

 ments, from the anterior part of which a narrow duct arises, that 

 runs towards the point of the upper jaw. This poison has an effect 



1 RAMDOHR Verdauungs werJcz. d. Ins. s. 204, 205, TREVIRANUS Verm. Schr. i. 

 s. 29 31, Tab. in. figs. 16, 17, TULK in Ann. of nat. Hist. xn. 1843, pp. 246248. 

 PI. iv. fig. 17. 



2 TREVIRANUS, in his work Ueber den innern Ban der Arachniden, s. 29, 30. Tab. 

 II. fig. 24, has described the intestinal canal imperfectly. BRANDT Mediz. Zool. II. 

 has partially improved on him. We follow here especially WASMANN in Abhand- 

 lungen hcrausgeyeben von den naturwissensch. Verein, Hamburg, 1846. I. 4to. s. 142 

 144. 



3 Syst. der vergl. Anatom. iv. s. 145. 



4 J. MUELLER in MECKEL'S Archivf. Anat. u. Physiol. 1828. s. 52. 



