56 MANUAL OF ZOOLOGY. 



system, or, indeed, of any other organs in addition to those 

 already described. Locomotion is effected with moderate 

 activity, but in an irregular manner, by means of the blunt, 

 finger-shaped processes of sarcode, or pseudopodia, which can 

 be protruded at will from any part of the body, and can be 

 again retracted within it. The pseudopodia also serve as pre- 

 hensile organs ; but they do not interlace and form a net- 

 work, nor do they exhibit any circulation of granules derived 

 from the endosarc, as in many others of the Rhizopoda. 



As regards the reproductive process in the Amoeba, no dif- 

 ferentiated sexual organs have hitherto been discovered, and the 

 true sexual form of the process is therefore unknown. Fresh 

 individuals, however, may be produced in three ways : 

 Firstly, by simple fission, the animal dividing into two parts, 

 each of which becomes an independent organism. Secondly, by 

 the detachment of a single pseudopodium, which becomes 

 developed into a fresh Amoeba. Thirdly, by the production of 

 little spherical masses of sarcode which may be derived from 

 the nucleus by fission, or may be produced by a segmentation of 

 the endosarc, the animal having previously become torpid, and 

 the nucleus and contractile vesicle having disappeared. These 

 little masses, however produced, develop themselves when 

 liberated into ordinary Amcebce. This last method of repro- 

 duction is obviously very closely analogous to the production 

 of " pseudonavicellse ;; in an encysted Gregarina. It has been 

 doubted, apparently with considerable reason, whether the so- 

 called Amoeba are distinct species of animals, or whether they 

 are not rather transitory stages in the life-history of other 

 organisms. It is quite certain that several of the Protozoa pass 

 through an Amoeboid stage, and it is also certain that vegetable 

 matter not uncommonly assumes similar characters (e.g., the 

 mycelium of certain fungi). It is therefore not impossible that 

 the forms known to the microscopist as Amoeba may be 

 ultimately discovered not to be permanent and distinct species ; 

 but the evidence on this head is still defective. 



It is certain, at any rate, that many organisms, both 

 vegetable and animal, pass through amoeboid stages consist- 

 ing, for a longer or shorter period, of protoplasm capable of 

 emitting " pseudopodia." It is certain, also, that such amoeboid 

 masses cannot be distinguished from true Amcebce, otherwise 

 than by their life-history. When, therefore, we are informed 

 that Amcebce can be shown to develop into different and higher 

 organisms, we must construe the statement as meaning nothing 

 more than that the higher organisms in question pass through 

 an " amoeboid " stage in the course of their development. 



