Il] AMOEBA 17 



pseudo- implies that they are not fixed organs like our own limbs, 

 but are made at any part of the surface of the body. When Amoeba 

 conies across anything it desires to eat, it throws out pseudopodia 

 on each side of it ; these then unite beyond the object, and so the 

 latter becomes engulfed, so to speak, in the body of the animal, 

 where it is digested. It may thus be said, that Amoeba flows round 

 its prey. Once the prey is inside, it is surrounded by a drop of 

 water poured out of the surrounding protoplasm or enclosed with 

 the food. There is probably some substance secreted into this 

 water which acts on the prey and dissolves it. The most recent 

 and careful study of Amoeba by Jennings has convinced him that 

 the throwing out of pseudopodia and movement generally are due 

 to changes in the ectoplasm, the endoplasm being passive. Local 

 contractions in the endoplasm seems the most probable cause and 

 when we study a slightly higher grade of animal we shall find that 

 these contractions are carried out by specialised threads called 

 myonemes. It is hard to resist the conviction that in the ectoplasm 

 of Amoeba, there is something corresponding to myonemes although 

 we cannot see them. The ectoplasm is a permanent skin; only where 

 it surrounds a food vacuole is it ever dissolved. The comparison 

 of Amoeba to an oildrop originally made by Butschli has proved 

 baseless. 



One of the most marked features in which Amoeba differs from 

 other animals, from ourselves for instance, is, that it possesses no 

 separate parts or organs, such as stomach, heart, lungs, etc., fitted 

 to perform the separate vital actions, or functions as they are 

 called. It breathes, that is, absorbs oxygen and gives off carbon 

 dioxide all over the body ; and it likewise excretes, that is, gets rid 

 of the oxidised protoplasm, at all points of the surface. If, however, 

 we are so fortunate as to come across a large Amoeba, which is 1 at 

 the same time comparatively clear of granules, and is moving only 

 sluggishly, we may be able to make out two definite objects in the 

 endoplasm. The first of these is called the contractile vacuole 

 (2, Fig. 1) ; this is a clear round space, which slowly enlarges and 

 then suddenly vanishes, and then reappears in the same place and 

 goes through the same series of changes. It has been suggested 

 that the cause of this appearance is that at a certain point in the 

 endoplasm a substance is produced by katabolism with a strong 

 affinity for water; this substance attracts to itself from the surround- 

 ing protoplasm water, carrying in it the soluble waste products, in 



S. & M. 'J 



