6 4 



MANUAL OF ELEMENTARY ZOOLOGY 



separately to the heart and is then sent forth again to the 

 tissues through the arteries. Oxygenated blood is therefore 

 called arterial. It is of a bright red colour. It will be 

 noted that the pulmonary artery contains venous blood, the 

 pulmonary vein arterial blood. It will also be seen that 

 the course of the circulation contains two circuits, one 

 short, passing through the lungs, and the other long, 

 passing through the rest of the body, the blood returning to 

 the heart between the two. This is shown on the Table on 



W.]d. 



Fig. 34. — A diagram of a kidney of the frog, to show the 

 arrangement of the tubules and blood vessels. One urini- 

 ferous tubule and h. portion of the vascular meshwork are 

 shown separately. In reality the blood vessels entangle the 

 tubules. 



cap., Capillaries; cold., collecting tubule; glom., glomerulus; M.cp., Mal- 

 pighian capsule ; m.c, the same more highly magnified ; ^c, peritoneum ; 

 r.a., renal artery ; r.p.v., branch of the renal portal vein ; r.v., branch 

 of a renal vein; ur.t., uriniferous tubule; ur.t'., places where other 

 uriniferous tubules open into the collecting duct; W.d., Wolffian or 

 kidney duct. 



p. 61. The two circuits are known respectively as the lesser 

 or pulmonary and the greater or systemic circulations. 

 The respiratory organs are engaged, as we have seen, 



in the excretion of carbon dioxide, and some 

 organB. ry water is also lost in the form of vapour through 



these organs. A further loss of water in a liquid 

 form and the excretion of solids dissolved in it takes place 

 through the kidneys. These are a pair of flattened, oblong, 

 dark red bodies which lie one on each side in the dorsal 



