328 



iTHE ANATOMY OF INVERTEBRATED ANIMALS. 



probably having the same function as in Scorpio.^ The 

 stomach gives otf caecal prolongations which may extend far 

 into the iimbs. There is usually a dilated short rectum, into 

 which the branched Malpighian ducts open. The nervous 

 system, more concentrated than that of the Arthrogastra^ is 

 reduced to a supra-oesophageal ganglion and a single post- 

 oesophageal mass, with four indentations on either side. There 

 are six or eight simple eyes in the anterior part of the cara- 

 pace. Auditory organs have not been discovered in these or 

 any other Arachnida. 



One of the most characteristic organs of the Ara7ieina is 

 the arachnidium^ or apparatus by which the fine silky threads 

 which constitute the web are produced. H. Meckel,'^ who 

 has fully described this apparatus as it occurs in Epeira dia- 

 dema, states that, in the adult, more than a thousand glands. 



Fig. 89, k.—MijgaU BloncUi (after Blancharc!).— The stomach with its cseca, and the 



remainder of the alimentary canal with the liver and Malpighian tubes. 

 Fig. 89, B.— The heart and arterial vessels of the same. 



with separate excretory ducts, secrete the viscid material, 

 which, when exposed to the air, hardens into silk. These 



* Lyonet's " Anatomie de differentes Especes d'Insectes" ("Mem. du Mu- 

 seum d'Histoire Naturelle," 1829) contains an elaborate account of this appa- 

 ratus, aswell as of the structure of the pedipalps of the male spiders. 



2 " Mikroafraphie einisrer Drnsenapparate der niederen Thiere." (Miiller's 

 " Archiv," 1846.) 8ee also BuCliholz and Landois. {Ibid., 1868.) 



