98 COMPARATIVE ZOOLOGY. 
rum." Had the blood not been filtered, the corpuscles 
aud fibriue would have mingled, forming a jelly-like mass, 
known as clot. Further, the serum will coagulate if heat- 
ed, dividing into hardened albumen and a watery fluid, 
called serostty, which coutains the soluble salts of the 
blood. 
These several parts may be expressed thus: 
(colored ) 
‘orpusel J 
Blood § role colorless) as ——— clog 
( Plasma (fibrine— (albumen. 
(serum (serosity = water and salts. 
If now we examine the nutritive fluid of the simplest 
animals, we will find 
only a watery fluid con- 
taining granules. In 
Radiates and the low- 
est Articulates and Mol- 
lusks, there is a similar 
fluid, with the addition 
of a few white corpus- 
cles. But there is no 
fibrine, and, therefore, it 
does not coagulate. In 
Fic. 62.—Nneleated Blood-cells of a Frog, x250. the higher Articulates 
and Mollusks, the circulating fluid resembles the chyle as 
we find it in the thoracic duct of Vertebrates, containing 
colorless nucleated cells, and coagulating.” In Verte- 
brates, there are, in addition to the 
plasma and white corpuscles of In- 
vertebrates, red corpuscles, to which 
their blood owes its peculiar hue. In 
Tishes, Reptiles, and Birds, 7. e., all 
the backboned animals born from 
eggs, these red corpuscles are nucle- 5... a_i pica eee 
ated; but in those of Mammals, no _ of the Frog, showing a 
white prominence at the 
nucleus has been discovered.” centre. 
mis 
35 
