258 



LECTURE XIX. 



110 „,e?* process into the base of the maxillary palpi (e), 



and of each thoracic leg (e'). A shorter diver- 

 ticulum (d) is continued from the upper part of 

 the stomach. The intestine is contracted where 

 it passes through the pedicle of the abdomen ; it 

 slightly expands in its straight course (y) along 

 the anterior part of that cavity, then contracts 

 and forms two short convolutions (<yr), and com- 

 municates with a large globular caecum (h), from 

 which the short rectum passes to the vent. Four 

 biliary ducts (i, i) open into each side of the 

 straight portion of the intestine. Two longer 

 and more slender urinary tubes (k, k) communi- 

 cate with the beginning of the caecum, which 

 - - - seems to stand to them in the relation of an 



Alimentary canal. Spider, ^^inary bladder. Lavge masscs of adipose epi- 

 ploon occupy, in well-fed spiders, the sides of the abdomen, and cover 

 and conceal the granular caecal terminations of the hepatic organ. 



The chyle is received immediately by the veins, and conveyed to 

 the dorsal vasiform heart. This organ is confined to the six dilated 

 anterior segments of the abdomen in the scorpions, where it is of 

 uniform diameter, except at its two extre- 

 mities : it receives the venous blood from the 

 surrounding pericardial sinus by ten or eleven 

 pairs of apertures, each guarded by a pair 

 of valves. From the anterior and larger 

 extremity the anterior aorta is continued, 

 which is short, and soon divides into three 

 branches : a longer and more slender vessel 

 is continued along narrow terminal segments 

 of the abdomen from the attenuated posterior 

 . end of the heart. 



1 In the spiders the heart (Jig. 111. «) ex- 

 1 tends, as in flying insects, along nearly the 

 whole of the abdomen, but is wider than in 

 the scorpion or in insects. It is fusiform, 

 with thick walls, composed chiefly of trans- 

 verse muscular fibres, slightly decussating on 

 the inner surface : a narrow strip of longi- 

 tudinal fibres extends along the middle of the 

 dorsal surface. 



The blood is returned to the heart by three or four veins (b, b) on 

 each side : it is propelled forwards by the contraction of the mus- 



Heart of Spider. 



