FOEMS AND SIZES OF BLOOD CORPUSCLES. 35 



In form, blood corpuscles are circular, oval, or ellipti- 

 cal, and, as already indicated, more or less flat and disk- 

 like. In all the Mammalia they are circular, except in the 

 Camel family in which they are elliptical. In Man their 

 two broad surfaces are somewhat concave, as plainly seen 

 in those which have their edges turned towards the observ- 

 er (Fig. 35). In some kinds of animals their two broad 

 surfaces are convex, as in the Ostrich, Triton, Stickleback, 

 etc. (Figs. 37, 38, 40). 



In some kinds of the Vertebrata, as in Man, the red cor- 

 puscles of the blood are so minute that it would take more 

 than 10,000,000 of them to cover a square inch of surface ; 



parts of the solid substance of the body which have been detached and car- 

 ried into the blood, and that this process is chiefly effected in what are called 

 the ductless glands, from whence the detached cells pass, as lympli, cmpusdes, 

 directly or indirectly into the blood." 



"The following facts are of importance in their bearing on the relation 

 between the different kinds of corpuscles : 



"(a). The invertebrate animals which have true blood corpuscles, possess 

 only such as resemble the colorless corpuscles of man." 



"(&.) The lowest vertebrate animal, the Lance-let (Amphioxus), possesses 

 only colorless corpuscles ; and the very young embryos of all vertebrate ani- 

 mals have only colorless and nucleated corpuscles." 



"(c.) All the vertebrated animals the young of which are born from eggs, 

 have two kinds of corpuscles colorless corpuscles, like those of man, and 

 large red-colored corpuscles, which are generally oval, and further differ 

 from those of man in presenting a nucleus. In fact, they are simply the 

 colorless corpuscles enlarged and colored." 



"(d.) All animals which suckle their young, have, like man, two kinds of 

 corpuscles colorless ones, and small, colored corpuscles the latter being 

 always flattened and devoid of any nucleus. They are usually circular, 

 but in the camel tribe they are elliptical. And it is worthy of remark, that 

 in these animals the nuclei of the colorless corpuscles become elliptical." 



" (e.) The colorless corpuscles differ much less from one another in size and 

 form, in the vertebrate series, than the colored. The latter are smallest in 

 the little Musk Deer, in which animal they are about a quarter as large as 

 those of man. On the other hand, the red corpuscles are largest in the Am- 

 phibia (or Frogs and Salamanders), in some of which animals they are ten 

 times as long as in man." HUXLEY, " Lessons in Elementary Physiology," 

 p. 69. 



