28 MORPHOLOGY OF PROTOZOA 



may become highly differentiated. A tough covering to the body, which 

 may be elaborately marked, is often developed from the ectoplasm, while 

 it is from this layer that the various permanent organs of locomotion such 

 as flagella and cilia originate. The ectoplasm also secretes the various 

 external coverings, such as shells and cysts. In the simpler Protozoa, 

 like the amoeba? and flagellates, the ectoplasm is merely a thin layer of 

 clear cytoplasm surrounding the endoplasm. It appears to be only 

 slightly more resistant than the endoplasm. In the more highly organized 

 ciliates and gregarines the ectoplasm is highly developed, and itself consists 

 of several distinct layers. It is a resistant membrane which enables the 

 organism to retain its shape. In any case, the most superficial layer of the 

 ectoplasm forms a delicate limiting membrane, the periplast. The surface 

 of the ectoplasm may be perfectly smooth, or it may be raised into a series 

 of longitudinal ridges. In other cases it is roughened, or may even develop 

 a series of symmetrical markings. In the amcebse, many of the simpler 

 flagellates, and many parasitic protozoa, the ectoplasm forms a complete 

 layer over the surface of the body, and when solid food is ingested this is 

 taken in at any part of the body. A particle comes in contact with the 

 ectoplasm which is gradually raised up round it, and finally closes over 

 it, so that the object, together with a certain quantity of liquid, is included 

 in a vacuole which sinks into the endoplasm. In other cases the solid food 

 particles are ingested in a similar manner at one particular spot on the 

 body surface. This occurs typically in certain flagellates, where solid food 

 appears to be ingested only at the base of the flagellum. In other flagel- 

 lates at this point there is a small excavation or pit in the ectoplasm into 

 which solid food is taken (Figs. 26 and 33). At the bottom of this pit the 

 food particle sinks into the endoplasm, and is included in a vacuole. This 

 depression is frequently of a permanent nature. In association with it 

 there may be special developments of the organs of locomotion which 

 create currents in the medium, so that food particles are directed into it. 

 In Chilomastix one of the flagella lies in a groove, at the posterior end of 

 which food particles enter the cytoplasm (Fig. 69). The opening in the 

 ectoplasm, which sometimes is capable of being opened and closed, is known 

 as the cytostome, while the funnel-shaped pit or tube leading from it to the 

 endoplasm is the oesophagus or cytopharynx. 



As already pointed out, the residue from the digestion of food material 

 within the food vacuoles is discharged through the surface of the body. 

 This may occur at any point on the body surface, but in the Ciliata there 

 may be a permanent opening in the ectoplasm, the cytopyge, which, how- 

 ever, is usually only visible when a food vacuole discharges its contents 

 at the posterior end of the body (Fig. 512). 



In some ciliates the cytostome is a simple opening on the surface of the 



