524 



COMPARATIVE ANATOMY 



CHAP. 



abdomen are distinctly separate, these invaginations may be repeated 

 in each. The whole mass of the mid-gut with its invaginations repre- 

 sents the digesting chylific stomach, and has glandular 

 walls. The liquid nourishment reaches to the very 

 extremities of these diverticula, which have been 

 inaccurately called hepatic tubes. 



Jl 



da 



FIG. 368. Digestive 

 tract of the Scorpion 

 (after Newport), pli, Phar- 

 ynx ; sd t salivary glands ; 

 md, diverticula of the mid- 

 gut ; vm, Malpighian ves- 

 sels; ed, hind-gut. 



FIG. 369.^, Digestive apparatus of Mygale caementaria 

 (after Duges in Cuvier's Regne Animal). B, The abdominal 

 portion of the same, from the side. C, Digestive apparatus 

 of a Gamasus, diagrammatic (after Winkler). Lettering the 

 same in the 3 figures : g, brain ; dt, enteric diverticula of the 

 thorax ; da, enteric diverticula (liver) of the abdomen (a), only the 

 portions entering into the abdominal mid-gut drawn ; md, mid- 

 gut with diverticula (d) of Gamasus ; vm, Malpighian vessels ; rb, 

 rectal vesicle (cloaca) into which both the digestive tract and 

 the Malpighian vessels enter ; o, oesophagus. 



The hind-gut is generally very short. It opens externally through 

 the anal aperture which is placed ventrally at the posterior end of the 

 body. Into the hind -gut enter tube-like excretory organs, corre- 

 sponding with the Malpighian vessels of the Antennata. There is 

 generally one pair of these, less frequently several pairs. In the 

 Acarina an unpaired excretory tube is often found. 



The fact that the Arachnoidea like the Antennata have Malpighian vessels, while 

 these vessels are not found in the Crustacea and Xiphosura and Pycnogonidce, is of 

 great importance in deciding the question of their systematic position. 



