48 MANUAL OF ZOOLOGY. 



more restricted, and to comprise a portion only of the body 

 (" villous region"). 



The " nucleus " is a solid granular body, one or more of 

 which is present within the endosarc of every Amoeba, but 

 its function is not known with any certainty. The " con- 

 tractile vesicles " are cavities within the endosarc, of which 

 ordinarily one only is present in the same individual, though 

 sometimes there are more. In structure it is a little cavity or 

 vesicle filled with a colourless fluid apparently derived from 

 the digestion, and exhibiting rhythmical movements of con- 

 traction (systole) and dilatation (diastole). In some cases radi- 

 ating tubes are said to have been seen proceeding from the 

 vesicle at the moment of contraction. Regarded functionally, 

 the contractile vesicle must be looked upon as a circulatory, 

 organ, and it offers therefore the most rudimentary form of a 

 vascular system with which we are as yet acquainted. 



Besides these proper organs, the endosarc usually contains 

 clear spaces, which are called " vacuoles," or, more properly, 

 " food-vacuoles." These spaces are of a merely temporary 

 character, and are simply produced by the presence of par- 

 ticles of food, usually with a little water taken into the body 

 along with the food. 



There are no traces of any organs of sense, or of a nervous 

 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 

 prehensile 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 



