or Red Disks of the Mammiferous Animals. 27 
puscles from the right ventricle, dried, all about 1-4-OOOth 
of an inch in diameter. 
11. Water Rat, adult, {Mus amphibius). Blood from both 
ventricles, examined dry; average-sized corpuscles l-4000th 
and l-3600th of an inch diameter. 
12. Common brown House Rat, a male, nearly full-grown, 
[Mus decumanus). Common size of corpuscles from right ven- 
tricle l-4000th to 1 -3554th of an inch, 
13. Common Mouse, (Mus micscidus). l-4000th and 
l-3600th common sizes. Extreme diameters l-5333rd and 
l-3000th. Blood from heart and vena cava. 
a. Foetus, about half an inch long, from the uterus of the 
above mouse. 1 -2666th the most frequent size, and many 
smaller corpuscles from l-5333rd to l-4000th, the latter being 
numerous. Many of the corpuscles more globular than usual, 
that is, more like spheres than disks, — a common appearance 
in the foetal blood of mammals at an early period. 
From this and several other observations, the comparatively 
large size of the blood corpuscles in the foetus becomes mani- 
fest. The fact is important, because it is connected with the 
comparative condition of the respirator}^ organs, and, more- 
over, illustrates the difference between the blood of the parent 
animal and that of the foetus; so that if there be any commu- 
nication between the vessels of the placenta and uterus, the 
blood of the mother and foetus is at all events different. 1 have 
examined the foetal blood of the human subject, obtained from 
the heart, placenta, and umbilical vessels, with the same result 
as above; and it appears to me to be of considerable interest*. 
14. Common Guinea Pig, adult male, [Cavia Cobay a). 
Corpuscles from the right ventricle, generally measuring 
from l-4000th to l-3200th of an inch. 
15. Domestic Rabbit, adult female, (Depus cunicultis). 
Most common diameter l-4000th; extreme sizes l-5000th 
and l-3200th of an inch. 
16. Golden Agouti, adult male, (Dasyprocta aurata). 
l-3600th the most common diameter. Extreme sizes l-5333rd 
and 1 -3200th. Blood from a vein of the ear. 
17. Acouchi, full-grown, (Dasyprocta acouchi). 1 -3600th 
a common diameter, as was also l-4000th. Extreme sizes 
l-4572nd and ] -3200th. 
18. White-whiskered Paradoxure, adult, (P, Deucomystax). 
Size of corpuscles very variable; most commonly l-4365th 
and l-4000th. Extreme diameters l-6000th to l-3200th. 
Blood from a prick of the tail. 
^ * The accurate Hewson observed the same fact in a fowl and in a 
viper. (Exp. Inquiries, part iii. p. 39.) 
