PROTOZOA 19 



Usually this can be done at any point of the surface, as in the familiar 

 case of Amoeba^ but most of those flagellates which perform amoeboid 

 ingestion do so in a particular region only. Other protozoa swallow 

 through a permanent mouth. The true mouth is the spot at which 

 the food passes below the ectoplasm. It may be (a) a bare patch of 

 endoplasm, (b) the opening of an excavation (oesophagus) in the 

 endoplasm, (c) the bottom of a depression (vestibule) in the ecto- 

 plasm, (d) the junction of a vestibule and an oesophagus. Any 

 passage, whether oesophagus, or vestibule, or compounded of both, 

 through which food enters is called a gullet, though not all cavities to 

 which this name is applied are actually used in feeding. The opening 

 of a gullet is the cytostome, which when there is a vestibule is not the 

 true mouth. Gullets are found in many of the Mastigophora and most 

 of the Ciliata. In ciliates either of the kinds may be present (p . 1 04) . In 

 the Mastigophora the gullet is at least sometimes ectoplasmic, but its 

 morphology needs further investigation. A gullet may be supported 

 by skeletal rods (Figs. 39 E, 89 A), and is then often dilatable: a 

 vestibule may have ciliary apparatus, trichocysts, etc. for taking food 

 (Figs. 39 C, 90). The Suctoria (Fig. i) draw the protoplasm of their 

 prey into their bodies through tentacles. The details of ingestion into 

 the protoplasm differ considerably in diflFerent organisms. In some 

 amoeboid forms the cytoplasm comes into contact with the food at 

 once, either by flowing over it or by its adhering to the surface and 

 being drawn in ; others enclose the particles to be swallowed without 

 touching them, either by arching over them, as Amoeba proteus does, 

 or by excavating a vacuole for their reception. In some at least of the 

 organisms whose food is driven into a gullet, a vacuole forms for it, 

 apparently by the pressure of the water forced in, and on reaching a 

 certain size nips off. Often, but by no means always, discrimination 

 is exercised between particles which appear equally capable of being 

 swallowed. It is doubtful whether this discrimination is concerned 

 solely with such properties as the size and shape of the particles or 

 also with their chemical qualities. Solid food is digested in food 

 vacuoles, which usually contain visible fluid and in which the reaction 

 is often first acid and then alkaline. Live food dies during the acid 

 phase, and protein is digested during the alkaline phase. Protozoa have 



chloroplasts of green plants). In this mode of nutrition the simple materials 

 of the food are absorbed through the surface of the body. In holozuic nutrition 

 complex organic substances are swallowed through temporary or permanent 

 openings as in the majority of animals. In saprophytic (or saprozoic) nutrition, 

 practised by certain organisms, including among others various parasites, 

 which are in contact with solutions of organic matter, relatively complex 

 carbon compounds are taken, but these are absorbed through the body sur- 

 face. The modes of nutrition classed under this head vary greatly in the 

 complexity of the substances they require. 



