516 Zoological Society. 
considerably above twice and a half greater than their breadth ; while 
in the Brown Owl the corpuscles are scarcely twice as long as they 
are broad. | 
“« Now both the absolute size of the latter, as well as the relation 
between their long and short diameters, approach very nearly to the 
dimensions frequently presented by the corpuscles of various birds. 
But in the Snowy Owl the corpuscles are not only peculiarly long, 
in proportion to their breadth, but their absolute length is much 
greater than is often to be found in the red particles of other birds, 
whether belonging to the rapacious order or not. Indeed it is pro- 
bable that the difference generally between the blood-disks of any’ 
two orders of birds is not greater than that now indicated between 
the disks of two species of one natural family, the Strigide. 
«* The corpuscles of the Snowy Owl, therefore, are very remark- 
able and characteristic, as any one may immediately see who will 
take the trouble to compare them with those of the Common Brown 
Owl. I have examined the blood of several other species of this 
family, and find the size and shape of the corpuscles of the Barn Owl 
(Strix flammea) to approximate most nearly to those of the Snowy 
Owl. 
“It will be seen that the nuclei of the blood particles of the 
Snowy Owl, exposed by acetic acid, were fully three times the length 
of their breadth; and it may be noticed incidentally, that in most 
birds the nuclei thus exhibited have a more elongated ellipse than the 
outline of their envelopes*. 
«We might expect to find an exact resemblance between the ele- 
mentary parts of such a truly natural family as the Columbide, and 
yet the observations show a striking difference between the blood 
corpuscles of the Passenger and Russet Pigeons, the average long 
diameter of the former being 1-1909th, and the short diameter 
1-4626th of an inch, while the latter are 1-2314th of an inch long, 
and 1-3429th broad. Although I have examined the blood of many 
different species of the Columbide, in no instance did the corpuscles 
agree in figure with those of the Passenger Pigeon; in the Turtle 
Dove (Columba Turtur) the long diameter appeared to be nearly simi- 
lar, but the short diameter agreed with that observed in the disks of 
the Russet Pigeon. Hence there was a remarkable difference in 
shape, and the corpuscles of the Passenger Pigeon, as far as I have 
yet ascertained, are quite peculiar, since the singularly narrow ellipses 
which they present have not hitherto been found in the red particles 
of other species of the Columbide. 
‘* It.should be recollected, however, that the results of my obser- 
vations may exhibit differences rather apparent than real, since our 
knowledge of the blood corpuscles is at present so limited, that we 
are not sure whether their size and shape may not be subject to some 
variation in relation to season, to the habits, or to certain conditions 
of the animal. In Man, and some of the other Mammalia, I have 
seen remarkable changes in the appearance of the blood corpuscles, 
* See Dublin Medical Press, No. 59, March 4, 1840. 
