1870. | AND ECONOMY OF THE LAMPREYS. 845 
those of Man, so commonly adopted, after Wagner, seems to demand 
reconsideration. Notwithstanding their correspondence in the cir- 
cular outline, they differ essentially in structure and size, in which 
respect the Lamprey’s red corpuscle truly conforms to the pyrenz- 
matous type. No blood-disks of any Apyrenzematous 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 Apyrenzemata. 
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-cor- 
puscles than any ever seen in this class. For, after my proofs that 
the Edentata are truly characterized by the largeness of these cor- 
puscles (Lecture ii. 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 Aprenzematous 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 Apyrenzmata the pale globules are commonly larger 
than the red corpuscles, in the Lamprey and other Pyrenzemata 
the pale globules are generally more or less smaller than. the red 
corpuscles. 

4000 ths. 4 =— es ofaninch. 
Of the above woodcut, fig. 1 represents the red corpuscles of 
Petromyzon planeri as seen in the liquor sanguinis—a, 6, 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 re- 
ferred 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 the blood of Man and of the Lampreys (Petromyzon 
planeri, P. fluviatilis, and Ammocetes 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 
