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Show 482 PROF. G. G U L L I V E R O N [June 15, Birds almost always have the corpuscles larger than those of Mammalia, here, too, are a few irregularities, as will appear on a comparison of the corpuscles of Linaria, Dolichonyx (fig. 61), and Trochilus (fig. 66) with the largest apyrensematous corpuscles (figs. 14, 23, and 47). In Birds the largest corpuscles belong to the Cursores (fig. 53), the next in size to the Rapaces (fig. 58), Palmipedes (fig. 65), Gral-latores, and the Hornbill (fig. 6 2 ) ; the smallest corpuscles occur in some of the little Granivorse (fig. 61) and Insectivorse, in the Humming- bird (fig. 66) and other Anisodactyli. Throughout the class of Birds there is so far a relation between the size of the species and the size of the corpuscles, that no instance is known of the largest corpuscles in the small species, or the smallest corpuscles in the large species. And herein this entire class rather resembles an order or family than the class of Mammalia ; and so, too, as regards the constant oval figure of the avian corpuscles. In some single apyrensematous orders there are greater diversities in the size, and in a few instances in the shape, of the corpuscles than in the entire class either of Birds or Reptiles ; in neither of these two pyrensematous classes is there any exception to the elliptical form of the corpuscles, nor are the corpuscles ever twice as large in one species as in another of the same class. APYRENSEMATOUS VERTEBRATES. As already described, in all the oviparous or pyrensematous Vertebrates there is a nucleus distinctly demonstrable in the red corpuscles. And now we come to the Mammalia or Apyrensemata, in which, on the contrary, no such nuclei can be made visible by the very same treatment which plainly displays them in the Pyrensemata; that is to say, a nucleus cannot be disclosed in the majority of the red blood-corpuscles of Apyrensemata. The oval blood-disks of the Camels (figs. 37-41) conform in this respect, and in smallness of size, to the circular corpuscles of other Apyrensemata ; in no pyrensematous vertebrate are the corpuscles so small as in the Camels. Of course we are not dealing now with the large temporary red corpuscles which have nuclei in the early mammalian embryo, nor with phases of development and decay in the adult, but with the majority of the regular corpuscles. Neither are we concerned with Mr. Wharton Jones's valid doctrine as to their origin, nor with any speculations as to their real nature. So far as is yet known this is peculiar; for the free apyrensematous corpuscles have no known homologue, and are devoid of the true characters of nuclei. Form of the corpuscles.-This is regularly a circular biconcave disk (figs. 1 and 2), the concavities very shallow and deepening towards the centre ; and this is characteristic of Apyrensemata. At the circumference the thickness is between a third and a fourth of the diameter of the corpuscle. But a body so soft, so readily affected by osmosis and other causes, is liable to assume many odd shapes which may be seen to occur during the examination. Thus appear such forms as plano-convex, biconvex, crenate, puckered, granulated, dinted, cup-shaped, and several others. Sometimes their circum- |
