136 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



the Musk-Deer, in which they are less than l-12000th of an inch in 

 diameter. It is in the Camel tribe alone that we find oval corpuscles 

 among Mammals ; these have about the same average length as the 

 round corpuscles of Man, but little more than half the breadth. In 

 Birds, the corpuscles are occasionally almost circular ; but in general 

 their diameters are to each other as 1J or 2 to 1. The size of the cor- 

 puscles is usually greater according to the size of the Bird ; thus among 

 the Ostrich tribe, the long diameter is about l-1650th of an inch, and 

 the short diameter l-3000th ; whilst among the small Sparrows, Finches, 

 &c., the long diameter is about l-2400th, and the short frequently 

 does not exceed half that amount. It is in Reptiles that we find the 

 largest red corpuscles ; and it is in their blood, therefore, that we can 

 best study the characters of these bodies. The blood-disks of the Frog, 

 from the facility with which they may be obtained, are particularly 

 suitable for the purpose ; their long diameter is about the l-1000th of an 

 inch, whilst their short or transverse diameter is about l-1800th. The 

 curious Proteus, Siren, and other allied species, which retain their gills 

 through their whole lives, are distinguished by the enormous size of 

 their blood-disks. The long diameter of the corpuscles of the Proteus 

 is about l-337th of an inch ; they are consequently almost distinguisha- 

 ble with the unaided eye. The long diameter of the corpuscles of the 

 Siren is about l-435th of an inch, and their short diameter about l-800th ; 

 the long .diameter of the nuclei of these corpuscles is about l-1000th, 

 and the short diameter about l-2000th of an inch, so that the nuclei 

 are about three times as long, and nearly twice as broad, as the entire 

 human corpuscles. 



217. The relation between the White or Colourless and the Red 

 Corpuscles of the Blood can only be determined by attentively watching 

 their development, and tracing them through all the stages of their 

 growth. Although our knowledge on this subject is far from complete, 

 yet there seems much reason to believe, from the observations of Mr. 

 Wharton Jones on the different forms of blood-cells presented in the 

 several classes of animals, and from those of Mr. Paget and other phy- 

 siologists on the several gradations of structure exhibited in the blood- 

 cells of Mammalia, that the red corpuscles have their origin in the 

 colourless, and that the different forms of blood-cell presented in diffe- 

 rent groups of animals are, in fact, progressive stages in the same de- 

 velopmental process, which may be checked at any one of them. Thus 

 among the lower Invertebrata, the cells which are observed to float in 

 their circulating fluid, seem to be little else than aggregations of gra- 

 nules, presenting a tuberculated surface ; no cavity can be distinguished ; 

 and it is with difficulty that the presence of a distinct cell-wall can be 

 demonstrated. This form, which is designated by Mr. Wharton Jones 

 as the "coarse granule-cell," presents itself also among the chyle and 

 lymph-corpuscles of Vertebrated animals, and is occasionally met with 

 in their blood. In other Invertebrata, the blood-cell undergoes a fur- 

 ther development ; for the cell-wall becomes more distinct, and the gra- 

 nules are so much more minute as to give to the entire cell a somewhat 

 nebulous aspect, its surface being now smooth instead of tuberculated. 

 This form of corpuscle, also, termed by Mr. Wharton Jones the " fine 



