64 MANUAL OF ZOOLOGY. 



In this case, however, the area of the general surface within 

 which an anus may be extemporised, appears to be more re- 

 stricted, and to comprise a portion only of the body (" villous 

 region"). 



The "nucleus" (fig. 8) is a solid granular body, or a clear 

 vesicle containing a " nucleolus " in its interior, one or more of 

 which is present within the endosarc of every Amoeba, but its 

 function is not known with any certainty. The "contractile 

 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 functionally, the contractile vesicle 

 may be looked upon as a circulatory organ ; in which case, it 

 offers the most rudimentary form of a vascular system with 

 which we are as yet acquainted. By others, however, the con- 

 tractile vesicle is believed to be filled with water from the 

 exterior, and it is regarded as a rudimentary form of water- 

 vascular system ; while others regard it as an excretory organ. 



Besides these proper organs, the endosarc usually contains 

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

 " food-vacuoles." These spaces (though sometimes rhythmic- 

 ally contractile) 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, 

 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 



