PROTOZOA I RHIZOPODA. 55 



charge 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 extemporised, appears to be more re- 

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

 region "). 



Fig. 4. A, Amoeba: developed in organic infusions (after Beale), greatly en- 

 larged; B, Ainceba princeps (after Carter) ; v Villous region ; c Contractile vesicle; 

 n Nucleus ; e Ectosarc. 



The "nucleus" (fig. 4) 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 " 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 

 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. 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. 



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 



