1897] MICROSCOPICAL JOURNAL. 85 



fishes and birds and mammals. The amphibia lie be- 

 tween a class acknowledged to contain widely varying 

 forms, some highly specialized, others exceedingly gen- 

 eralized. The variation in size of red corpuscle corre- 

 sponds with this range in form. They are small in caBcil- 

 ians, 18'2xl5 very large in amphiuma, a salamander. 



There is another striking change in this series. The 

 normal absence of the nucleus from the mammalian red 

 corpuscles and the presence of it in all other red corpus- 

 cles is well-known. A brief consideration of the func- 

 tion of the red coll helps in explaining this fact. It is 

 no longer a typical cell, it is very highly specialized for 

 one purpose, to take up oxygen, the more oxygen it can 

 carry the more efficient it is. H.-vmoglobinc is the essen- 

 tial oxygen carrier in the corpuscle, by crowding out the 

 nucleus more of this substance can be present, hence the 

 corpuscle becomes more efficient. A series can be made 

 showing the gradual loss in different animal forms, large 

 in amphibians, it is reduced to small size in birds and in 

 mammals is gone entirely. Decrease in size follows the 

 same law. Exchange is far more rapid between small 

 masses than between large ones, and small cell elements 



