of Edinburgh , Session 1880-81. 
29 
5. Theory to account for certain movements exhibited by 
low forms of Animal Life, and termed Amoeboid. By 
John B. Haycraft, Senior Demonstrator of Physiology in 
the University of Edinburgh. 
A large number of unicellular plants and animals, and many of 
the cellular units which make up the complex tissues of man and 
more evolved animals, exhibit certain movements. These are 
termed “ Amoeboid,” as they are well seen, and were at an early 
period studied in the Amoeba. 
If an amoeba or a white blood corpuscle of the newt be examined 
with a good lens, the following facts, among others, may be made 
out. The corpuscle looks like a granular lump of jelly containing 
two or three nuclei, and it is, we will suppose, spherical to begin 
with. Soon the shape changes, for a little process is seen to pro- 
trude at one side, which may become retracted, or go on elongating. 
In the substance of the cell and in the processes, movements may 
be observed, consisting evidently of a flowing of the protoplasm, 
as indicated by the embedded granules which are carried along. 
The little processes are termed pseudopodia, and vary much in 
shape, some being thick and either pointed or club-shaped, others 
are filamentous, as in the perforated Foraminiferse, where large 
numbers of these are seen radiating from the test. These move- 
ments may be automatic, and they are modified by various external 
forces ; for example, heat and electricity. 
I shall now endeavour to account for the throwing out and sub- 
sequent retraction of these little pseudopodia, pointing out, it may 
be, but one factor, but that a probable one. 
Various theories have been already advanced (Briicke, Hermann, 
Engelmann), which, for want of a better name, we may call geome- 
trical : they would account well enough for the protrusion of pro- 
cesses had we the slightest evidence to suppose the imagined struc- 
tures to exist. 
The simplest of these supposes that, if at a certain spot on the 
surface of the cell a pseudopodium is to be protruded, contraction 
occurs along a chord of the segment, including this spot. Such a 
contraction could no doubt produce a protrusion, but it is gratuitous 
