95 



Ruminants the smallest corpuscles are found ; yet some of tlie largest 

 species have corpuscles larger tlian those of many Carnivora, and of 

 the Horse. The Camelida are the ouly mammals with oval hlood- 

 discs, likę those of the lower Vertehrata in shape, but uniformly 

 smaller ; and in structure the corpuscle of the Camels is exuctly the 

 šame as the corpuscle of other Mammalia, being destitule of a nu- 

 cleus corresponding to that which is so obvious in the corpuscle of 

 lower animals. Among the Rodents, the corpuscles of the Capybara 

 are as large or slightly larger than those of Man ; the Harvest Mouse 

 has smaller corpuscles than any other Rodent, and in the order 

 generally their size is about the šame as in the Lemurs. Of the Eden- 

 tata, the T\vo-toed Sloth has the largest corpuscles, after those of the 

 Elephant, of any mammal ; those of the Armadillo are about the šame 

 in size as those of the Monkeys. The corpuscles of the Marsupiata 

 agree generally in form and size with the corpuscles of the corre- 

 sponding placentai mammals. In the Monotremata, according to 

 the observations of Dr. Davy, Dr. Hobson, and Dr. E. Bedford, the 

 corpuscles are of the šame form and about the šame size as in Man. 

 An examination which I made of the corpuscles of the Echidna -vvas 

 to the šame efFcct, but I had not an opportunity of applying a micro- 

 meter to them. 



OviPAfioos Vertebrata. 



In birds and reptiles, -vvith a few exceptions, the corpuscles are 

 oval, the long diameter being commonly rather less than twice the 

 short diameter. These proportions used to be considered as univer- 

 eal, but they are not so ; for the long diameter of the corpuscles of 

 birds and reptiles may either be nearly thrice or scarcely one and a 

 half of the short diameter ; and it is remarkable that these difFerences 

 of form are occasionally presented in the corpuscles of nearly aUied 

 genera, as more particularly explained in the Proc. Zool. Soc. 1840, 

 pp. 43 and 132 ; and 1842, p. 110. In osseous fishes, as Professor 

 Wagner has noticed, the corpuscles are generally not much longer 

 than broad ; I commonly found a few amcmg them of a circular shape, 

 and he observed the majority of them of this figure in the blood of 

 the Cyclostomes. In some species of other orders the corpuscles are 

 about twice the length of their breadth ; in the Pike they are some- 

 \vhat angular and pointed at the ends ; and on the whole the corpus- 

 cles of fishes are extremely variable in shape. The diameter of the 

 circular corpuscles of mammals is very frequently about the šame as 

 the short diameter of birds' corpuscles. They are largest in the 

 Amphibia generally ; and largest of all in the Amphibia vvith perma- 

 nent gills, as discovered some years ago by Professor Wagner. My 

 measurements of the corpuscles of the Siren agree -vvith his vie\v. 



Nucleus. — This exists permanently in the blood-corpuscle of the 

 lower Vertebrata, but only for a short time in that of mammals, not 

 excepting even the Camelidte. It is only during the earlier period of 

 intra-uterine life that the corpuscle of mammals has a nucleus corre- 

 sponding to the permanent one in the corpuscle of lower animals. In 

 birds, the nucleus, \vhen exposed by a vveak acid, is commonly longer 

 in proportion to its breadth than the envelope ; but there are some 



