OF THE BLOOD. 219 



therefore, depends on some other circumstance than a difference 

 in the size of the animal. 



As to their shape, I have already mentioned that they are 

 flat in all animals, even in the human subject ; of which any 

 one may be convinced by repeating the following experiments. 



EXPERIMENT I. 



Take a small quantity of the serum of human blood, and 

 shake a piece of the crassamentum in it till it is coloured a 



diameter may be either thrice, or scarcely one and a half of the short 

 diameter; and it is remarkable that these differences of shape may 

 occur in the corpuscles of nearly alhed genera, as explained in the 

 * Proceedings of the Zoological Society,' 1840, pp. 43, 132; and J842, 

 p. 110. The short diameter of birds' corpuscles is commonly about 

 the same as the diameter of the circular corpuscles of mammals. The 

 size of the blood-corpuscles of mammalia in connexion with that of the 

 animal, is described in a former part of this note'. Throughout the 

 entire class of birds, the law for the size of the corpuscles is very nearly 

 the same as in a single family of mammals. At least my measurements, 

 given at the end of this chapter, afford but few if any examples of com- 

 paratively large corpuscles in the smallest species, and of more minute 

 corpuscles in the largest species of birds. In a humming bird, Dr. Davy* 

 found the average length of the corpuscles 2^Vs tD an d the breadth 

 joV o tn of an inch. These corpuscles are therefore shorter than those, 

 yet examined, of any other bird. In my Tables of Measurements in 

 this class, it will be observed that the blood-corpuscles of that great 

 bird, the cassowary, are the largest, while the smallest corpuscles 

 occur in some of the little insectivorous and granivorous birds, and 

 in a few of the smallest species of the gallinaceous order. 



In the naked amphibia the blood-corpuscles are generally larger than 

 in any other animals ; and largest of all in the amphibia with perma- 

 nent gills, as discovered by Professor Wagner, b and confirmed by my 

 measurements of the corpuscles of the siren. 



The blood-corpuscles of fishes are noticed in Note cxvn ; the thickness 

 of the corpuscles of mammals, and their comparative size and shape in 

 the embryo, in Notes xcv and cxvi ; the structure of the corpuscles of 

 mammalia and lower vertebrata, in Note en ; the central spot, in 

 Note xcvi ; the shape of the nucleus in oviparous vertebrata, in 

 Notes cv and cxvn ; irregularities in the figure of the corpuscles of 

 mammals, in Notes cvi, ex and cxi ; and the blood-corpuscles of in- 

 vert ebrat a, with the corpuscle in its different phases of development in 

 the animal series, in Note xci. For the copious Tables of Measure- 

 ments, see Note cxvm*, at the end of this chapter, pp. 237 et seq. 



a Proceedings of the Zoological Society, b Physiology, tr. by Dr. Willis, p. 236 ; 

 March 24, 1846. and Proc. Zool. Soc. 1837, p. 107. 



