COMPARATIVE SIZES OF RED CORPUSCLES OF BLOOD. 127 



the diameter averages l-3280th of an inch ; in the Dog, l-3540th ; in the Bear, about 

 l-370Uth ; in the Weasel, l-4200th; in the Cat, l-4400th ; and in the Viverrce, l-5365th. In 

 two species only of the Cctacea, have the blood-discs been yet examined ; the Dolphin, in 

 which their diameter averages 1 -3829th of an inch ; and the great Rorqual (the largest known 

 Mammal), in which they are only l-3100th of an inch, or scarcely larger than those of Man. 

 Among the Pachydermata, the average excluding the Elephant (the diameter of whose blood- 

 discs is about 1 -2745th of an inch), and the Rhinoceros (in which they are about l-37G5th), 

 may be stated at about 1 -4200th; and there is less variation than might have been expected, 

 from the different size "and conformation of the several species examined. Among the Rib- 

 minantia, the corpuscles are for the most part smaller than in other orders ; and there is more 

 relation, between their diameter and the size of the animal, than is elsewhere observable. 

 Excluding the Camelidae (which are zoologically intermediate between the Ruminantia and 

 Pachydermata), we find a range of sizes extending from the l-3777th to the l-12,325th of 

 an inch; the former is the diameter in one of the larger Deer; the latter in the Musk Deer, 

 which is the smallest in the whole order. In the Camel tribe, the average of the long dia- 

 meter of the corpuscles is about 1 -3300th of an inch , whilst that of the short diameter is 

 l-6300th; and this is nowhere widely departed from: the length of the discs is, therefore, 

 not quite twice their breadth. Among the Rodentia, the discs are rather large, especially 

 considering the small size of most of the species. In the Capybara, which is the largest 

 animal of the order, they average 1-3 190th; and in the Mouse family (the smallest of Mam- 

 malia), they are as much as l-3S14th. In the Squirrels, the diameter is rather less; but in 

 scarcely any of the whole order is it under 1 -4000th. Among the Edentata, the Two-toed Sloth 

 has been found to have corpuscles of the unusually large diameter of l-2865th of an inch; 

 whilst in the Armadilloes they average about l-3400th. In the Marsupialia the range is 

 nearly the same as among the Rodentia. 



b. In BIRDS, according to the observations of Mr. Gulliver, the long and short diameters 

 of the corpuscles usually bear to each other the proportion of 1^ or 2, to 1; and this is the 

 general relation among Oviparous Vertebrata, with the exception of some of the Crocodile 

 tribe, in which the length is sometimes three times the breadth. The size of the corpuscles 

 of Birds has generally more relation to that of the species, than it has in Mammalia. No 

 instance has yet been detected, of the occurrence of comparatively small corpuscles in the 

 larger species, and of large corpuscles among smaller animals, which has been seen to be 

 common among the former class ; the blood of the Humming-birds, however, has not yet 

 been examined. The largest discs are found among the Cursores; those of the Ostrich have 

 an average long diameter of l-1649th of an inch, and a short diameter of 1 -3000th; and 

 among the larger Raptores, Grallatores, and Natatores, the dimensions are but little inferior. 

 The least dimensions hitherto observed are among the small Passerine birds ; in which the 

 corpuscles have a long diameter of about 1 -2400th of an inch, and a transverse diameter of 

 from l-3SOOth to l-4SOOth. Circular discs may be occasionally observed in some species, 

 agreeing with the others in every particular but their form ; and every gradation may be no- 

 ticed between these and the regular oval corpuscles. 



c. The large size of the blood-discs in REPTILES, especially in Batrachia, and above all, 

 in the Percnnibranchiate species of the latter, has been of great service to the Physiologist ; 

 by enabling him to ascertain many particulars regarding their structure, which could not 

 have been otherwise determined with certainty. Among other facilities which this occa- 

 sions, is that of procuring their separation from the other constituents of the blood ; for they 

 are too large to pass through the pores of ordinary filtering-paper, and are therefore re- 

 tained upon it, after the liquor sanguinis has flowed through. The blood-discs of the warm- 

 blooded Vertebrata cannot be thus separated. The oval corpuscles of the Frog have a long 

 diameter of about 1-1 108th, and a transverse diameter of about l-1800th of an inch; those 

 of the Salamander or Water-newt are still larger. The long diameter of the corpuscles of the 

 Proteus is stated by Wagner at l-337th of an inch ; that of the Siren is about l-435th, the 

 short diameter being about 1-SOOth of an inch; the extremes of variation, however, are very 

 wide. The long diameter of the nuclei is about 1-1 000th or l-1100th, and the short diame- 

 ter about l-2000th; hence it is about three times as long, and nearly twice as broad, as the 

 entire Human blood-disc, thus having six times its superficies; its thickness is about l-3800th 

 of an inch. 



d. The number of FISHES, in which the diameters of the blood-discs have been examined, 

 is still inconsiderable. In the common Perch, theyaverage l-2100th by 1-2824 ; in the Carp, 

 they are l-2142nd of an inch by 1 -3429th; in the Gold-Fish, though of the same genus and 

 of much smaller size, they are as much as l-1777th by l-2824th; in the Pike, 1 -2000th by 

 1 -3555th; and in the Eel, 1-1 745th by 1-2 842nd.* 



* A summary of Mr. Gulliver's numerous and valuable observations is contained in the 

 Proceedings of the Zoological Society, No. CLII. 



