166 BIOLOGY OF THE PROTOZOA 



to the receptive area at the base of the flagellum (Kent), but accord- 

 ing to France granules on the inside of the collar are moving away 

 from the cell as defecatory material while the food particles move 

 down the outside to a receptive area not included by the collar 

 base (Fig. 92, D). 



In the majority of corticate flagellates the food-taking receptive 

 area is continued as a pit or groove known as the flagellum fissure, 

 or as the cytopharynx. The flagellum arises usually at or near the 

 base of such a pit and in many cases the contractile vacuole empties 

 into it. 



It is in the ciliate group, however, that we find the most character- 

 istic and most complicated types of cytostome. Here they may be 

 mere pores in the cortex which remain closed except during the 

 process of ingestion and without accessory current-producing motile 

 organs, or they may be permanently open and provided with undu- 

 lating membranes or other vibratile elements. The former type, 

 known as the Gymnostomina, eats only occasionally and then by a 

 definite swallowing process, the soft mouth region widening into 

 a huge opening to receive the prey. Thus Didinium nasutum ordi- 

 narily swims about with little evidence of a mouth at the extremity 

 of the conical proboscis (Fig. 98, p. 187), but when swallowing a 

 Paramecium which may be larger than itself, the entire anterior 

 end appears to be nothing but mouth, the body wall of the Didinium 

 being reduced to a thin enveloping sheath about the Paramecium 

 (Figs. 98, 5). Similar, but not so spectacular cytostomes are present 

 in other types of Gymnostomina. Spathidium spathula may swal- 

 low smaller ciliates like Colpidium (Fig. 99, p. 188); Nassula aurea, 

 Chilodon cucullus, etc., still smaller forms. In all such forms 

 the protoplasmic region around the mouth is strengthened by 

 simple or complex metaplastic structures— the trichites (Fig. 195, 

 p. 475). The Trichostomina are always provided with food-getting 

 motile organs and a constant stream of water with suspended bac- 

 teria and other minute living things passes through the permanently 

 open mouths making these creatures, according to Maupas, gluttons 

 par excellence of the animal kingdom (see, however, p. 190). 



The complications in regard to structure in these two types of 

 cytostome have to do with the support of the walls of the mouth 

 and of the gullet into which the mouth opens, and for the perfection 

 of the current-producing apparatus. Such support is obviously 

 important in preventing rupture of the soft protoplasmic bodies of 

 forms like Didinium nasutum, Enchelys farcimen, Prorodon tires 

 or Spathidium spathula (Fig. 99, p. 188). In all of these cases there 

 is an armature of elongated rods, trichites, formed of stereoplas- 

 mic substances, embedded in the walls of the mouth and gullet, 

 and these, like spiles in a ferry slip, take up the strain when the 

 mouth is opened. In many cases, however, the perfection and 



