90 THE ANATOMY OF VERTEBRATED ANIMALS. 



but, in all other known Vertebrata, the blood contains corpus 

 cles of two kinds. 



In Ichthyopsida and Sauropsida^ both kinds are nucleated ; 

 but one set are colorless, and exhibit amasboid movements, 

 while the others are red, and do not display contractility. 

 Except in the Marsipohranchii^ which have round blood-cor- 

 puscles, the red corpuscles are oval. They attain a larger size in 

 the perennibranchiate Ampliibia than in any other Vertebrates, 



In Maminalia^ the blood-corpuscles are also of two kinds, 

 colorless and red, the colorless possessing, and the red being 

 devoid of, nuclei. It is but very rarely that a nucleated cor- 

 puscle, with a red color especially developed about the nu- 

 cleus, is seen in Mammalian blood ; but such cases do occur ; 

 and, from this and other circumstances, it is probable that the 

 Mammalian red corpuscle is a free-colored nucleus. 



The colorless corpuscles of Maiiirrialia are spheroidal, and 

 exhibit amaeboid movements ; the red corpuscles are flattened, 

 usually circular, but sometimes oval ( Camelidw) disks, devoid 

 of contractility. 



TJie Lymp)hatic System. — This system of vessels consists, 

 chiefly, of one or two princijDal trunks, the thoracic duct, or 

 ducts, which underlie the vertebral column, and communicate, 

 anteriorly, w^ith the superior vence cavse, or with the veins 

 which open into them. 



From these trunks, branches are given oif, which ramify 

 through all parts of the body, except the bulb of the eye, the 

 cartilages, and the bones. In the higher Vertehrata, the 

 larger branches are like small veins, provided with definite 

 coats, and with valves opening toward the larger trunks, while 

 their terminal ramifications form a capillary net-work ; but, in 

 the lower Vertebrates, the lymphatic channels assume the form 

 of large and irregular sinuses, which not unfrequently com- 

 pletely surround the great vessels of the blood-s^^stem. 



The lymphatics open into other parts of the venous S3's- 

 tem besides the affluents of the superior cavse. In Fishes 

 there are, usually, two caudal lymphatic sinuses wliich open 

 into the commencement of the caudal vein. In the Frog, foui 

 such sinuses communicate wuth the veins, two in the coccy* 

 goal, and two in the scapular, region. The walls of these si 

 nuses are muscular, and contract rhythmically, so that they re- 

 ceive the name of Lyinphatic hearts. The posterior pair of 

 these hearts, or non-pulsating sinuses corresponding with 

 them, are met with in Heptilla and Aves, 



