AND PHYSIOLOGY. 



241 



427. Ventral T r u 21 k . — The blood which is driven forwards 

 by this dorsal vessel is collected by a set of vessels which unite 

 into a large tube called the Ventral vessel, or trunk, which 

 returns it to the posterior part of the body. 



428. Blood of Articulates, — This fluid called blood is a 

 thin liquid, yellowish brown, red, green, or even colorless, 

 and never containing corpuscles ; and the only reason why it 

 is called blood is, that it circulates like the blood of the 

 higher animals. 



429. Chylaqucous Fluid, — But besides this fluid there is 

 another found in the general or abdominal cavity of the body, 

 which, though not contained in organs expressly designed for 

 its circulation, yet is rapidly carried th ough the body by 

 means of the motion of the different segments of the animal, 

 which in many of this order is incessant. This fluid, unlike 

 the true blood, is rich in corpuscles and easily coagulated, 

 which gives it one of the essential characteristics of true blood 

 in the higher animals. It, however, must probably be re- 

 garded as the cylaqueous fluid of many of the lower verte- 

 brata. Scorpions have arteries and veins. 



430. Heart and Blood fig. 244. 



of Crustacea.— Among the 

 crustaceans, such as the crab 

 and lobster, we find a vessel 

 much shorter than the dorsal 

 vessel of most articulata, 



Which resembles a heart from Blood Corpuscles of the Crab. A, Granule 



the fact that it is a propel- Cells " B ' Nucleuted Ceilb - 

 ling organ and has muscular fibers in its coats. The blood in 

 these animals is of a whitish or purple color, and the pulsa- 

 tions of the heart vary in number from fifty-one to two hun- 

 dred per minute. 



427. How is the blood returned that is circulated by the dorsal heart? 

 the blood of articulates. 429. What other fluid is found in these animals ? 

 6aid of the heart and blood of the crab and lobster ? 



42S. Describe 

 430. What is 



