44 MANUAL OF ZOOLOGY. 



the body by a process of intussusception ; any portion of the 

 surface being chosen for this purpose, and acting as an ex- 

 temporaneous mouth. When the particle of food has been 

 received into the body, the aperture by which it was admitted 

 again closes up, and the discharge of solid excreta is effected 

 in an exactly similar manner. In this case, however, the 

 area of the general surface within which an anus may be ex- 

 temporised, appears to be 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 

 contraction (systole) and dilatation (diastole). In some cases 

 radiating tubes are said to have been seen proceeding from 

 the vesicle at the moment of contraction. Regarded func- 

 tionally, the contractile vesicle must be 16*oked upon as a cir- 

 culatory 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 

 particles 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 pre- 

 hensile organs ; but they do not interlace and form a network 

 as in many others of the Ekizopoda. 



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 



