IN RELATION TO ZOOLOGICAL DISTINCTION. 53 



Worm-Miiller, Transf. u. Pleth, Christiania, 1875; Otto, Archiv f. ges. 

 Physiologic, 1884, xxxiv, 233; Vierordt, Daten u. Tabellen, 1906, 205, 

 206; Ellenberger, Physiologie d. Haussaugethiere, 1890, 181; Claisse et 

 Josue", Compt. rend. soc. biologic, 1896, XLVIII, 1020; and Harris, Journal 

 of Physiology, 1903, xxx, 319). See table 20. 



The erythrocytes are, except in the elephant, more numerous per cubic 

 millimeter in mammals than in birds, amphibia, reptiles, and fish, and gen- 

 erally they are much more numerous. In birds they are more numerous than 

 in cold-blooded animals, and they are least numerous in the salamander 

 and certain of the amphibia, in which the proportion may fall to a mere 

 fraction of the average in warm-blooded animals. Among mammals the 

 number is highest in the camel tribe, next highest in the sheep and goat, 

 and lowest in the elephant. There is not any numerical distinction of the 

 ruminants from other classes of ungulates, nor does there appear to be 

 anything definite in the way of numerical differences between the ungu- 

 lates, carnivora, and rodents. Considerable addition to our data must be 

 made before any figure can be accepted as the mean for any species, except 

 possibly in the case of the human being. Among the cold-blooded animals 

 the differences are in some instances so marked as to be positive in showing 

 generic peculiarities, as, for instance, the differences in the members of the 

 group of Amphibia, the differences between the osseous and cartilaginous 

 fishes, and the differences between the lizard and salamander. The num- 

 ber of corpuscles is, however, probably of less importance than the per- 

 centage of hemoglobin within them. 



THE SIZE OF THE ERYTHROCYTES IN RELATION TO GENERA. 



While the erythrocytes of specimens of blood from different individuals 

 of a given species may vary as much as 40 per cent or more in either direc- 

 tion from the mean diameter, a very large proportion in most if not all 

 bloods of mammals falls within narrow limits of the mean measurements, 

 and in different individuals of the same species the mean measurements 

 are of such uniformity as to justify their acceptance as reliable standards 

 of comparison and differentiation. The cells of the new-born have a some- 

 what larger diameter than those of the adult, and they have a larger range 

 of measurement; the range in the female is greater than in the male. 



The mean diameters of the red corpuscles of different species vary 

 within wide limits (table 21), the smallest corpuscles thus far examined 

 being those of the musk-deer (2.1 (i, Gulliver), and the largest those of 

 the amphiuma (69.8 to 41.4 p, Gulliver), which may be seen by the unaided 

 eye. In many instances, however, the differences may be so slight, even 

 in species and genera far removed from one another, as to be valueless of 

 themselves in zoological differentiation. Nevertheless, it is probable that 

 in no two species are the mean diameters exactly the same, and even when 

 they are so close as to be practically identical there may be certain peculi- 

 arities, such as the extent of the range in size, the constant occurrence of 

 erythrocytes of unusual dimensions, obscure appearances in the cells which 

 have been expressed by the term "individuality," etc., which may be 

 determining. 



