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Show 1875.] RED BLOOD-CORPUSCLES. 485 Mammal. It would be very interesting and probably instructive to examine the corpuscles of the Sirenia. Reverting summarily to a few points throughout the whole apyrensematous class, we shall find several plain facts which, though long since demonstrated, are still ignored in the current treatises of comparative anatomy and histology. For example, while the smallest corpuscles occur in the Ruminants, there are some species of this order in which the corpuscles are larger than in certain Ferse ; the Edentates, on the other hand, are eminently characterized by the largeness of the corpuscles; commonly the diameters of the apyrensematous corpuscles agree remarkably with the short diameters of the corpuscles in Birds. The corpuscles in a few Apyrensemata are five times as large as in others ; and even in the single order of Ruminants the corpuscles, besides aberrations in their shape, are thrice as large in several Cervidse and Bovidse (fig. 35) as in some Tragulidse (figs. 29 and 30). In the Ferse the corpuscles are more than twice as large in some species as in others, in this order the largest corpuscles (fig. 14) being larger than those of M a n (fig. 1), and the smallest (figs. 18 and 19) smaller than in some Ruminants (figs. 35 and 36). Hence, on the whole, there are greater diversities in the size of the corpuscles than in any other class ; so that in this point of view a single apyrensematous order would appear equal to an entire class either of Birds or Reptiles, and each of these two pyrensematous classes only equivalent to an order of Mammalia. But comparing the largest with the smallest batrachian corpuscles, and those oi Lepidosiren and some Rays and Sharks with the smallest corpuscles in osseous fishes, differences of size appear almost or quite as great as in Apyrensemata. From this class selections might be and have been made to show that there is no relation between the size of the species and the size of the corpuscles. These are quite as large in the tiny Harvest-Mouse (fig. 46) and Shrew (fig. 10) as in the great Giraffe (fig. 36) and Horse (fig. 26). But if, instead of thus comparing such widely different animals, and excepting some little irregularities already noticed, we confine the observations to small natural groups of the class, such a relation will plainly appear in a rule that the largest corpuscles occur in the large species and the smallest corpuscles in the small species of a single order or family. This relation is well shown by the Ruminants, Rodents, and Edentates ; and even in the Ferse, which offer some exceptions, the largest corpuscles are found in the big Seals (fig. 14), and the smallest corpuscles in the little Viverras and Paradoxures (figs. 18 and 19), In fine, though this rule is applicable only to single orders or lower sections of Apyrensemata, it extends to the whole class of Birds, but neither to Reptiles, Batrachians, nor Fishes, except in some partial instances, which seem to be rather indeterminate or accidental than regular. In the following Tables the measurements are all in vulgar fractions of an English inch, and express only the average diameters of the red blood-corpuscles or their nuclei. The numerator, being invariably 1, |