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Show 1875.] RED BLOOD C O R P U S C L E S . 479 except in the Lampreys; largest in the tailed Batrachians and Lepidosiren ; and then follow, in the order of the size of the corpuscles, Rays and Sharks, Frogs and Toads, Reptiles, Birds, and osseous Fishes, with certain exceptions, which may be seen in the Tables of Measurements. Among the oval corpuscles, whether in Pyrensemata or Apyrensemata, a few may deviate by gradations to the circular shape. Of these terms Pyrensemata and Apyrensemata, here applied to the two great sections of the Vertebrate subkingdom, an account is given in m y Lectures cited above, also in the second volume of the ' Journal of Anatomy and Physiology,' in the ' Proceedings of the Zoological Society,' Feb. 25, 1862, and in the ' Hunterian Oration,' 1863. FISHES. In no other vertebrate class are the red blood-corpuscles so difficult to measure as in this, wherein they are prone to rapid septic conditions, are singularly delicate in outline and substance, and hence most liable to changes of shape ; in all of which points the corpuscles of Fishes contrast remarkably with those of Reptiles and Birds. Form of the corpuscles.-Throughout the Vertebrates this is a disk, like a cake or coin ; and hence the term blood-disk ; but it is never so thin proportionally as a coin, and in fishes the thickness is about one third of its short diameter. The corpuscles are circular in the Lampreys, as figured with details in the ** Proceedings of the Zoological Society,' Dec. 6, 1870, p. 845 ; but in all other fishes more or less oval, so far as we yet know. If we consider the short diameter of the corpuscle as 1, the long diameter will usually be between 1^ and 11; and the nucleus has much the same figure, and is often nearly or quite globular. But these proportions are variable, since the corpuscles are frequently suboval; and in such cases several of them assume, by gradations, a circular shape, while those of the suboval form predominate. This may be plainly seen, for example, in the Anacanthini, especially a few hours after the death of the fish ; and then, in other orders besides that, the corpuscles are apt to present angular, fusiform, lanceolate, crescentic, oat-shaped, and still more irregular forms, all of which commonly exist in the blcod of Gadidse and Clupeidse obtained from fishmongers. In some Acanthopteri and Malacopteri, as Scomber, Caranx, Lophius, and Salmo, and the great Eels of Rodriguez, good examples occur of well-defined oval corpuscles. In the Pike most of them are somewhat pointed at the ends. In the osseous fishes there is generally, but not always, a rounded projection on each broad surface of the corpuscle, caused by the nucleus and a groove between it and the margin of the disk. And in no Pyrensemata has the regular red corpuscle that concavity, gradually deepening towards the centre (Plate LV. fig. 2), which is characteristic of the regular corpuscle in Apyrensemata, and has often been mistaken for a nucleus. Size of the corpuscles.-In the osseous fishes the largest corpuscles are those of the Salmonidae, as figured in the ** Proceedings of the Zoological Society,' Nov. 19, 18/2, p. 835; but though this largeness is plain in Salmo, Trutta, and Thymallus, it disappears in |