THE GENERAL PHYSIOLOGY OF THE PROTOZOA 189 



(6) Holozoic Nutrition. In this type of assimilation three series 

 of events must be distinguished, each of which may be effected by 

 means of special organs : the capture and ingestion of the prey ; its 

 digestion ; and lastly the rejection from the body of the non- 

 nutritive residue (defaecation). 



The methods of food-capture and ingestion have been dealt with 

 above in a general way. As regards food - capture, methods of 

 prehension by means of pseudopodia, or by special adhesive organs, 

 such as the suctorial and raptorial tentacles of Acinetaria (p. 457) 

 the tongue of Didinium (p. 442), etc., must be distinguished from 

 methods whereby the food is wafted towards the body in currents 

 produced by special vibratile organs such as flagella and cilia. As 

 regards ingestion of food, a distinction is imposed by the nature of 

 the outer surface of the body-protoplasm, whether naked or invested 

 by a firm cortex or cuticle. 



In naked forms the food is ingested at any point, by methods 

 which vary in different forms. In Amodba proteus the hinder end 

 of the body is most active in ingestion ; hi Actinosphcerium all points 

 on the surface are equally active. Rhumbler (204) distinguishes 

 four methods of food-ingestion in amoebae : (1) By " import," when 

 the food is drawn into the protoplasmic body as soon as it comes 

 into contact with it, and with sca^ely any movements on the part 

 of the amoeba (Fig. 23) ; (2) by flowing round, " circumfluence," in 

 which the protoplasm, as soon as it comes into contact with the 

 food-particle, flows round it on all sides and engulfs it ; (3) by 

 " circumvallation," when the amoeba, while still at some distance 

 from the object, sends out pseudopodia which, flow towards each 

 side of the prey, and ultimately meet round it and surround it com- 

 pletely, without ever having been in actual contact with it ; (4) by 

 " invagination," in which the amoeba touches and adheres to the 

 object, and the portion of the ectoplasm in contact with it is 

 invaginated into the endoplasm like a tube, the walls of which 

 become liquefied and fused together, so that the food-particle is, 

 as it were, sucked into the endoplasm (Fig. 82). Of these various 

 methods, the process of circumvallation is most suggestive of a 

 conscious and purposeful act on the part of the amoeba ; but a 

 remarkable parallel to it is seen in the penetration of Lankesterdla 

 into a red blood-corpuscle, as described by Neresheimer (see p. 378, 

 infra). In this case, as soon as the parasite comes within .a certain 

 distance of the corpuscle, the latter opens its arms, as it were, to 

 the parasite, and engulfs it in a manner very similar to the 

 ingestion of food by circumvallation on the part of an amoeba. 

 In both cases the object that is ingested must give off some substance 

 which exerts at a certain distance an effect on the protoplasm of 

 the cell which ingests it. 



