328 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



probably having 1 the same function as in Scorpio. 1 The 

 stomach gives off cascal prolongations which may extend far 

 into the limbs. 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-cesophageal ganglion and a single post- 

 cesophageal 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 Aranehia is 

 the arachnidium, or apparatus by which the fine silky threads 

 which constitute the w r eb are produced. H. Meckel, 3 who 

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

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



A B 



Fig. 89, k.—Mygale Blondii (after Blanchard).— The stomach with its caeca, and the 



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

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



with separate excretory ducts, seerete the viscid material, 

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



1 Lyonet's "Anatomic de dim' rentes Especes d'Tnsectes" ("Mem. du Mu- 

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

 ratus, as well as of the structure of the pedipalps of the mnlc spiders. 



2 " Mikrographie einisrer Druaenapparate der niederen Thiere." (Muller'a 

 " Archiv," 1846.) See also Buchholz and Landois. (Ibid., 1868.) 



