RECENT MEMOIRS ON FRESHWATER llHIZOPODA. 285 



alteration of the body-contour. Locomotion is effected in 

 two ways. In one case it takes place by contractility, affect- 

 ing the whole body-substance in a uniform degree. By this 

 mode the body alters in contour but little and glides along 

 by virtue of a constantly rotating motion of its superficies 

 over the surface of the objects on Avhich it finds itself {e. g. 

 Hyalodiscus). In other cases it is only restricted portions of 

 the surface by the agency of whose contractility locomotion 

 is effected, either by a flowing ouAvards of the body-substance 

 or by the projection of sometimes pointed, sometimes blunt, 

 pseudopodia, by aid of which the organism draws or pushes 

 itself onwards. When a test is formed the place of origin of 

 the pseudopodia becomes limited to definite parts of the 

 body ; if naked they may be given off from any part of 

 the Avhole body-superficies. Under all circumstances the 

 jjseudopodia are simple prolongations of the body-substance, 

 into which they can flow back just as they imperceptibly 

 take origin from it. They are not only organs of locomo- 

 tion, but, like the body-plasma, possess the faculty to digest 

 foreign bodies — in some forms whose shell does not alloAV of 

 the passage inwards of large objects as '^ food,'^ not only 

 their capture but their digestion is performed by the pseudo- 

 podia. 



The food is taken bodily into the substance of the 

 organism, and becomes embedded directly in the protoplasm. 

 Any definite apparatus serving to the formation of any 

 digestive fluid is quite absent. It is true that captured 

 objects become embedded in a vacuole and surrounded by a 

 fluid, but this cannot be regarded as a special digestive organ, 

 since it originates and disappears "with the coming and going 

 of its contents. Any once-for-all preformed place, by pos- 

 sibility to be designated as a mouth, does not exist ; but any 

 exposed part of the superficies (body or pseudopodia) can 

 incept foreign bodies. There does not seem except in rare 

 cases any particular choice of food, though some forms are 

 very, if not wholly, abstemious, whilst others are all but 

 insatiable. 



In many Amoebce the differentiation into an outer homo- 

 geneous and an inner granular substance which exists has 

 been held to indicate a differentiation into a contractile 

 cortical, and a medullary region, the latter performing the 

 digestive function, still the distinction is no decisive one, but 

 is gradual, inasmuch as the transition of one substance into 

 the other is imperceptible and there exist no definite sharp 

 limits between them. 



A whole series of organisms do not advance beyond the 



