642 



ZOOLOGY 



SECT. 



divided internally by folds into a series of eight chambers ; into 

 each of these chambers the blood passes by a pair of valvular 

 apertures or ostia. The heart ends both in front and behind in 

 main arteries, the anterior and posterior aortce (ant. art., post, art.) ; 

 and a series of pairs of lateral arteries are given off from the various 

 chambers. The anterior aorta soon bifurcates to form a pair of 

 vessels which embrace between them the oesophagus, and meet 

 below in a median ventral trunk which runs backwards above the 

 nerve-cord. The blood carried to the various parts of the body 

 by the arteries is gathered up into a large ventral sinus from which 

 it passes to the book-lungs. From these it is carried by a series of 



veins to the pericardial sinus to 

 enter the heart through the 

 ostia. 



The organs of respiration 

 in the Scorpions are in the form 

 of pulmonary sacs or book-lungs 

 (pul.), the stigmata or external 

 openings of which have already 

 been referred to. Each pul- 

 monary sac is a compressed 

 chamber lined with a thin 



chel 



stomo- 



saigld 



mesent 



mat 



-jbroct 



fw]b die 



cuticle. The lining membrane 

 is raised up into numerous 

 delicate laminae lying parallel 

 with one another like the leaves 

 of a book. Into the numer- 

 ous narrow spaces between the 

 laminae the air penetrates, and 

 oxygenates the blood which 

 enters the interior of the laminae 

 from the ventral sinus. 



A pair of coxal glands, situated 

 near the base of the fifth pair 

 of appendages, are, in the 

 embryo Scorpion, represented 

 in the second to the sixth segments by tubes which grow out from 

 the ccelomic sacs ; in the adult Scorpion only the one pair persists, 

 in the form of a closed gland, and its function is quite uncertain. 



The nervous system is constructed on a plan which bears a 

 considerable resemblance to that of the Crayfish and that of the 

 Cockroach. There is a bilobed cerebral ganglion or brain (Fig. 546, 

 brn.) from which nerves are given off to the eyes ; a nerve-collar 

 formed of a pair of cesophageal connectives unites ventrally in a 

 sub-cesophageal ganglion, forming the anterior part of a ventral nerve- 

 cord (ne. co.). The connectives and sub-oesophageal ganglion give 

 rise to the nerves of the first six pairs of appendages and of the 



FIG. 547. Dorsal view of the internal organs 

 of Scorpion, chel. chelicerse ; hep. liver ; 

 hep. du. hepatic ducts ; mal. Malpighian 

 tubes ; mesent. mesenteron ; proct. intestine ; 

 sal. gJd. salivary glands : stomo. stomodseum. 

 (From Leuckart, after Elan chard.) 



