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Show 1875.] RED BLOOD-CORPUSCLES. 481 a few species longer, and in more smaller than in some of the Anura. Thus in most Tortoises and Crocodiles and the Slow-worm the corpuscles are longer than, though not so broad as, in the Green Tree- Frog and in some exotic Toads, but are smaller in Python, Teius, Zootica, Lacerta, Plestiodon, and Iguana tuberculata than in any Batrachians ; and of this Iguana, which has the smallest known reptilian corpuscles, it is remarkable how much smaller they are than those of Iguana cyclura. Nor are the corpuscles in Reptiles, though regularly larger than in Birds and Osseous Fishes, ever quite so large as in Rays and Sharks; and in some Ophidians and Saurians the corpuscles are smaller than in certain Salmonidse. There is more uniformity of the corpuscles throughout the class of Reptiles than in some single orders of Apyrensemata; in no Reptile are the corpuscles twice the size of those in other reptiles, and the corpuscles are oval in every species. Here, again, there is a conformity of Birds to Reptiles, and a divergence of both these classes from Mammalia, each of those pyrensematous groups being in these respects more like an order than the class of Apyrensemata. But Reptiles, unlike Birds, present no relation between the size of the corpuscles and that of the species; they are as large in the little Viper and Snake as in the huge Pythons and Boa, and in the small Anguis and Chamaleon as in the large Teius and Monitor. Differences in the size of the corpuscles probably occur at certain seasons. BIRDS. Form and size of the corpuscles.-They are oval in all birds, gene* rally flat, with a slight tendency to be gibbous on the broad surfaces, altogether of much the same shape as in reptiles; taking the short diameter of the avian corpuscles as unity, the long diameter would usually vary between 1| and 2. But, as in Reptiles so in Birds, there are remarkable deviations from the regular proportions ; thus, e. g., in Columba migratoria (fig. 60), Lanius excubitor (fig. 56), and Syrnea nyctea (fig. 58) the length exceeds twice the breadth of the corpuscles, while in Columba rufina(Hg. 59) and a few more pigeons, Dolichonyx oryzivorus (fig. 61), in species of Loxia and certain other: Granivorse, the corpuscles have a much shorter oval figure. A mere glance at the Tables of Measurements will show how nearly the short diameters of the blood-disks of Birds agree with the diameters of the blood-disks in Apyrensemata; so that there is no bird in which such coincidence with some mammals is not obvious. Regularly the nucleus is more oblong than the entire corpuscle, so that the length of the nucleus is about twice, and occasionally nearly or quite thrice, its breadth. Hence this elongated shape exceeds that of the corresponding nucleus of other Pyrensemata, and is characteristic of Birds ; but there are exceptions, as may be seen in some gallinaceous species, in which the nucleus is suboval or nearly glo- ' Though in Birds the red corpuscles are regularly smaller than those of Reptiles, a few exceptions occur; for example, the corpuscles are quite as large in the Cassowaries as in certain Saurians. And while PROC. ZOOL. Soc-1875, No. XXXI. 31 |