19 
they possess a higher organization than the Water species, and if rightly 
named, we must give up the notion hitherto entertained that Amoeba pro- 
toplasm is as structureless "as a speck of jelly," moving and feeling 
without "organs," and reproducing itself by simple division of its 
homogeneous substance. The Land Amoeba has a dense and contractile 
ectosarc, or outer layer, which however is not distinctly separable from 
the inner granule-bearing substance or endosarc. Its mode of reproduction 
is by internal evolution of germs. In other respects it agrees with the 
Water Amoeba, alimentation being carried on by gradual enclosure within 
its substance of the food (diatomacese, &c. ) with which it comes in contact. 
Carter and others had already noticed, even in the Water species of 
Amoeba, a partial differentiation of the plasm into outer (dense) and inner 
(soft) layers. In Greefs Land Amoeba, the outer substance besides 
becoming denser, has acquired a specialized power of contraction and 
relaxation, so regulated that when contraction commences at any point of 
the surface of the animal's body, relaxation takes place at some opposite 
point, either simultaneously or at the preceding moment, the effect of this 
consentaneous action being, that the whole mass of protoplasm composing 
the endosarc is driven in the direction of the yielding portion of the ectosarc. 
By this means the creature is enabled to make its way through the 
interstices of the loose earth or sand in which it has its being. And since 
this regulated movement may occur at any part of the surface, the creature 
appears to have the power of governing its movements. It is more pro- 
bable, however, that the direction in which movement takes place, depends 
on the circumstance, that porous earth offers least resistance where inter- 
stices between its particles occur, and thus allows the contents of the body 
to be pressed forwards by the vis a tergo of the contracting segment, 
although even this explanation implies something like conscious sensation 
at the surface of the animal's body. The significance, we might almost 
say the motive, of this peculiar " adaptation to circumstances " is not far 
to seek when we consider the particular habitat and mode of life of the 
earth-dwelling Amoeba. 
But the interest of the case centres in this : that a change in the atomic 
constitution of the exterior plasm of the Land Amoeba, scarcely amounting 
to what we may call differentiation of parts, in the sense of "organs," 
supplies the means by which a peculiar rythmical motion is obtained. The 
contractility of the whole protoplasmic substance is transferred as it were 
to the ectosarc, and the now specialized power is exerted for a special 
purpose. This definite action and direction of the contractile ectosarc is 
