1878.] Ameba Proteus. 235 
AMCEBA PROTEUS. 
BY PROF, JOSEPH LEIDY. 
wonderful creature is the Amw@éa, one of the lowliest of the 
lowest class of animals, a mere speck of the thinnest jelly 
endowed with the usual attributes of all living things. Possessing 
an. extensile and contractile power, it puts forth portions of its ma- 
terial in any direction; which portions act as temporary instru- 
ments of locomotion and prehension, and which again withdrawn, 
melt away in the common mass without leaving a trace of their 
previous existence. 
The human body with its intricate mechanism and appliances 
is a theme of incessant wonder and admiration, but the Amadéa in 
its simplicity of structure and capabilities may reasonably excite 
the same feelings. Though it has long been known, it has recently 
acquired new interest, from the discovery in higher animals of 
jelly-specks which in structure and endowments are undis- 
tinguishable from the free Amada of stagnant waters. The 
white corpuscles of the blood travel through the tissues of our 
body as independent beings, just as the Ameéa creeps in the mud - 
of a pool, and so alike are they that the wandering corpuscles ap- 
pear as if they were parasitic Am@de. 
With such a creature as an Amba, of the utmost simplicity, 
a globule when quiet; of the most variable and ever changing 
shape when moving, one would not anticipate the recognition of 
different kinds, of the character of the more fixed specific forms 
of higher animals. Nevertheless, we observe, Amæbæe varying 
greatly in size, in the general habitual shape they assume in mo- 
tion, in the extent and usual form of the locomotive prolonga- 
tions,and in some other points, ordinarily sufficient to render dif- 
ferent kinds distinguishable from one another. 
Many naturalists think that all varieties of Amade are transi- 
tory phases of one and the same species, and this view is in some 
Measure confirmed by the occurrence of intermediate or transi- 
tionary forms which make it impossible, in many cases, strictly to 
define the limits of more characteristic and striking forms such as 
we commonly find. The same reasoning, however, applies with 
more or less force to higher organic forms, and as with these, it 
is at least convenient to refer to the different kinds of Amabe as 
SO many named species. 
vr. XII—NO. IV 
