150 ANIMAL PHYSIOLOGY. 
time, aggregations of very minute granules (elementary gran- 
ules) may be seen. These are supposed to represent the disin- 
tegrating protoplasm of the corpuscles. 
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Fie. 146.—Blood-plaques and their derivatives (Landois, after Bizzozero and Laker). 1, red 
blood-corpuscles on the flat; 2, from the side; 3, unchanged blood-plaques ; 4, lymph- 
corpuscle surrounded with blood-plaques ; 5, blood-plaques variously altered ; 6, lymph- 
corpuscle with two masses of fused blood-plaques and threads of fibrin; 7, group of 
blood-plaques fused or run together ; 8, similar small mass of partially dissolved blood- 
plaques with fibrils of fibrin. 
The pale or colorless corpuscles are very few in number in 
mammals compared with the red, there being on the average 
only about 1 in 400 to 600, though they become much more 
numerous after a meal. They are granular in appearance, and 
possess one or more nuclei, which are not, however, readily seen 
in all cases without the use of reagents. They are character- 
ized by greater size, a globular form, the lack of pigment, and 
the tendency to amceboid movements, which latter may be ex- 
aggerated in disordered conditions of the blood, or when the 
blood is withdrawn and observed under artificial conditions. 
It will be understood that these cells (leucocytes) are not con- 
fined to the blood, but abound in lymph and other fluids. 
They are the representatives of the primitive cells of the em- 
bryo, as is shown by their tendency (like ova) to throw out 
processes, develop into higher forms, etc. In behavior they 
strongly suggest Amoeba and kindred forms. 
We may, then, say that in all invertebrates the blood, when 
it exists, consists of a plasma (liquor sanguinis), in which float 
the cellular elements which are colorless; and that in verte- 
brates in addition there are colored cells which are always nu- 
cleated at some period of their existence. The colorless cells 
