PROTOZOA 15 



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. Its opening 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. 97). 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, 88 A), and is then often 

 dilatable: a vestibule may have ciliary apparatus, trichocysts, etc. for 

 taking food (Figs. 39 C, 89). Not all so-called gullets however are 

 used as such. 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 different 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. 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 appear not to digest 

 fat. Defaecation of the indigestible remains of food takes place at any 

 part of the surface when there is no pellicle, but in pelliculate forms 

 at a fixed spot. Sometimes there is a permanent rectal passage lined 

 by ectoplasm (Fig. 87 B, an). Saprophytic forms range from some, 

 such as Polytoma, which can subsist on mixtures of substances as 

 simple as aminoacids and acetates, to parasites whose food probably 

 differs chemically but little from that of holozoic forms. 



Reserve materials, for use at times when nutriment is not being 

 taken or when some process, such as rapid multiplication, is making 

 heavy demands upon the resources of the organism, are stored by 

 most protozoa, and are often conspicuous, as granules, vacuoles, 

 crystals, etc., in the cytoplasm. The carbohydrates starch, para- 

 mylum (in the Euglenoidina), and leucosin (in the Chrysomonadina) 

 are formed by holophytic organisms and by some colourless forms 

 related to these (as by Polytoma, Fig. 24, Peranema, etc.). Glycogen 

 is stored by parasitic and other anaerobic forms, in which it is per- 

 haps split with evolution of energy, as in various anaerobic metazoa. 



