!M)2 Zoological Society. 



corpuscles, the Hyaena* would be arranged with the CanidiE, Basaris 

 with the Ursidcs, and Cercoleptes with the Viverridce. It is curious 

 that the Fox has slightly smaller corpuscles than the Dog. In the 

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

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

 the Horse. The Camelidte are the only mammals with oval blood- 

 discs, like those of the lower Vertebrata in shape, but uniformly 

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

 same as the corpuscle of other Mammalia, being destitute 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 same as in the Lemurs. Of the Eden- 

 tata, the Two-toed Sloth has the largest corpuscles, after those of the 

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

 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 placental mammals. In the Monotremata, according to 

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

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

 An examination which I made of the corpuscles of the Echidna was 

 to the same effect, but 1 had not an opportunity of applying a micro- 

 meter to them. 



Oviparous Vertebrata. 



In birds and reptiles, with 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- 

 sal, 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 allied 

 genera. In osseous fishes, as Professor Wagner has noticed, the 

 corpuscles are generally not much longer than broad ; I commonly 

 found a few among 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 somewhat angular and pointed 

 at the ends ; and on the whole the corpuscles of fishes are extremely 

 variable in shape. The diameter of the circular corpuscles of mam- 

 mals is very frequently about the same as the short diameter of birds' 

 corpuscles. They are largest in the Amphibia generally ; and largest 

 of all in the Amphibia with permanent gills, as discovered some years 

 ago by Professor Wagner. My measurements of the corpuscles of 

 the Siren agree with his view. 



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

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



* It is remarkable that the extent of the streaked muscular fibre of the gullet 

 of the Hyjena is the same as in the Viverridce, which differ in this respect from 

 the Canidce, and still more from the Ursidte. It would be interesting to examine 

 the oesophageal muscular sheath of the Kinkajou. 



