290 CLASS AMPHIBIA. 



the kidney to which it is taken by the renal -portal veins or 

 through the liver by the anterior abdominal vein. Vertebral 

 (azygos) veins are very generally present, opening into the 

 superior venae cavae. 



The question of the homology of the inferior vena cava with the piscine 

 veins is difficult to settle. From its relations to the kidneys and from 

 the condition in Dipnoi, it would appear to be one or both of the posterior 

 cardinals. The difficulty in the way of this view is that it does not, so far 

 as is known, develop from the posterior cardinals which are always present 

 in the embryo. 



In Proteus and Siren some of the pulmonary blood is retiu-ned into the 

 vena cava inferior (Hyrtl). 



The red blood corpuscles are nucleated. They are oval in 

 shape and of considerable size, reaching in Amphiuma in their 

 greatest diameter -r^th mm. 



The lymphatic system consists of vessels and sinuses. There 

 is a large subcutaneous lymph sinus, especially well developed 

 in the Anura, and a large subvertebral sinus enveloping the 

 aorta, kidneys, etc. The lymphatic vessels open into the great 

 veins, and near the point of opening are often dilated into mus- 

 cular contractile chambers, the lymph-hearts. In the frog there 

 are two pairs of these ; a posterior pair placed near the hind end 

 of the urostyle and opening into the femoral veins, and an 

 anterior beneath the suprascapulae and opening into the sub- 

 scapular veins. In the Urodeles the posterior pair alone is 

 present. There are no lymphatic glands along the course of 

 the vessels as in birds and mammals, but patches of lymphatic 

 tissue, in which amoeboid cells are set free, are present in different 

 parts of the body. 



A spleen, usually placed in the mesentery near the stomach, 

 is present. 



The Urinogenital Organs * are constructed on the same 

 type as those of Elasmobranchs. The kidney is an elongated 

 gland (except in Anura) with persistent nephrostomes and with 

 a duct to which the collecting tubules pass. In the male there 

 is a testicular network, through which the sperm passes from 

 the testis to some of the kidney tubules. The kidney duct 

 serves therefore as vas deferens as well as ureter. It opens 



* Spengel, J. W. Arheiten a.d. Zool. Inst. Wilrzburg, 3, 1876, p. 1. 

 Brauer, A. " Entwick. der excretionsorgane der Gymnophionen," Zool. 

 Jahrb. (Anat.), 1902, 16, p. 1. 



