184 



ANATOMY OF VERTEBRATES. 



CHAPTER XIX. 



CIRCULATING SYSTEM OF BIRDS. 



§ 152. Blood of Birds. — The blood is hot and of a deep red 

 colour. The blood-discs are more abundant than in the cold- 

 blooded Vertebrates, save, perhaps, in some Ophidia : they are 

 nucleated, elliptic, and flattened in form; averaging in size, in 

 long diameter -j-^-^th, in short diameter ^gVe^th, of an inch; 

 with the following observed extremes : — Humming-bird, long 

 diameter -^-g-g, short diameter xoVo ' Ostrich, long diameter y-gV-g, 

 short diameter -goVo- Milne-Edwards notes decimally the fol- 

 lowing range of size in different species of the class : — ^ Long 

 diameter, maximum, 1*59; minimum, 1*105: short diameter, 

 maximum, 1*110 ; minimum, 1*158.'^ (Metrical system.) 



The blood-discs are largest in the embryo, losing size as the 

 respiration gains in activity and extent in the progress of the in- 

 dividual to maturity. The smaller size of the blood-discs of Birds 

 as compared with those of cold-blooded Ovipara exemplifies the 

 same inverse ratio of their size to the amount of respiration. The 

 j)roportion of organic matters contained in the water of the blood 

 is greater than in the Hcematocrya, as will be seen by comparing 

 the subjoined Tables with those in vol. i. pp. 463, 464 : — 



ccxxxix. p. 86. 



** CCLXV. p. 64. 



' lb. p. 27. 



