844 MR. GULLIVER ON THE ANATOMY [ Dec. 6, 
T. venustus (as characterized, 7. ¢. s.) cannot be considered really di- 
stinct from 7’. viridis. We have specimens of this bird now before 
us from Rio, Bahia, Matto Grosso, Eastern Venezuela, and Bugotd, 
and can find no constant differences amongst them, although there 
is considerable diversity of tint in the colour of the lower back, and 
some specimens approach to what Dr. Finsch has recently proposed 
to call T. eyanurus (P. Z.8. 1870, p. 559). 
On the other hand three Panama skins (in Mus. S.-G.) present 
the remarkable character of the outer tail-feathers above mentioned. 
The first outer pair are all pure white except a narrow basal patch 
concealed by the tail-coverts. Of the second pair, considerably more 
than the apical half is white. In the third pair the white apices 
measure 2 in. in length. When the tail is closed the under surface 
appears perfectly white. We therefore call this bird 7. chionurus. 
We have seen other examples of this Panama species in Mr. Law- 
~rence’s and Mr. Gould’s collections. 
10. On certain points in the Anatomy and Economy of the 
Lampreys. By Grorcre Guitiver, F.R.S. 
BLOOD-CORPUSCLES. 
Red Corpuscles.—For the discovery of the now well-known cir- 
cular shape of the red blood-corpuscles of the Lamprey, we are 
indebted to that eminent physiologist Rudolph Wagner. He 
likened them, as biconcave disks and otherwise, to those of Man and 
Mammalia; and as his figures and descriptions of those of the 
Lamprey are the only ones with which I am acquainted, it seems to 
me that a further account of them is yet desirable. 
The majority of them are circular; only a few assume a slightly 
oval form, just as some circular red disks appear among the far 
greater number of the regular oval or suboval ones of osseous fishes. 
The red corpuscles of the Lamprey are but rarely or exceptionally 
biconcave disks, and then only from irregular or unequal depressions 
on the surfaces, scarcely ever from those two syinmetrical concavities 
which are so truly characteristic of the blood-disk of Apyrenaematous 
vertebrates. On the contrary, the red blood-corpuscles of the 
Lamprey are regularly either flat or slightly biconvex (fig. 1, a and 4); 
but this form is liable to much variation from one or more dents 
caused by puckering or contractions inwards either of the surface 
or of the margin of the soft disk ; often a depression on one side and 
projection of the other produces a concavo-convex form; and, as a 
rule, the disk is proportionally and absolutely thicker than that of 
Apyrenzematous vertebrates. 
The nucleus (fig. 2) is very distinct, either circular or suboval, and 
sufficiently thick to prevent two such central depressions on the faces 
of the red corpuscle as would make it a symmetrical biconcave disk. 
Hence the comparison of the blood-disks of the Lamprey to 
