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Show 1870.] AND ECONOMY OF THE LAMPREYS. 845 those of Man, so commonly adopted, after Wagner, seems to demand reconsideration. Notwithstanding their correspondence in the circular outline, they differ essentially in structure and size, in which respect the Lamprey's red corpuscle truly conforms to the pyrensematous type. No blood-disks of any Apyrensematous vertebrate are known to be either regularly nucleated, so large, or so thick as those of the Lamprey ; nor is the flat or slightly biconvex form of this fish's blood-disks the regular shape of those of the Apyrensemata. But though the size may and does, so far as is yet known, thus afford a good diagnostic of existing vertebrates, it does not necessarily follow that Mammalia have never lived with much larger red blood-corpuscles than any ever seen in this class. For, after m y proofs that the Edentata are truly characterized by the largeness of these corpuscles (Lecture iii. Med. Times and Gaz. Sept. 13, 1862; Proc. Zool. Soc. Feb. 10, 1870), it seems highly probable that the huge and extinct species of this Aprensematous order had blood-disks quite as large as those of the Lamprey. Pale Globules, fig. 3.-Of this fish these globules are of the same shape, size, and structure so well known in other vertebrates; and hence, while in Apyrensemata the pale globules are commonly larger than the red corpuscles, in the Lamprey and other Pyrensemata the pale globules are generally more or less smaller than the red corpuscles. 40(10 ths -* 1 ' ! ! 1 ' ! • ! ' oranlndv. Of the above woodcut, fig. 1 represents the red corpuscles of Petromyzon planeri as seen in the liquor sanguinis-a, b, corpuscles of regular shape seen edgewise ; fig. 2, red corpuscles with their nuclei exposed by the action of sulphurous acid ; and fig. 3, pale globules of the blood. They are all drawn, like the engravings referred to in the Proc. Zool. Soc. Feb. 10, 1870, to a scale of which each division stands for one four-thousandth of an English inch. Size of the Corpuscles.-In the following measurements are given, in vulgar fractions of an English inch, the average dimensions of the corpuscles of tbe blood of Man and of the Lampreys (Petromyzon planeri, P. fluviatilis, and Ammocoetes branchialis). There is so little difference between the blood-copuscles of these fishes that one description may serve for all three of them. Formerly I accidentally |