STRUCTURAL DIFFERENTIATIONS 157 



cell. According to the older interpretation these protoplasmic 

 collars assist in food-taking b>' forming a sticky directive course 

 for particles down the inside to the receptive area at the base of the 

 flagellum (Kent), but according 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. 82, 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 (Euglenida, etc., Figs, 85, 95). 



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

 istic and most complicated types of c;vi'ostome. 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 ^'ibratile elements. The former tA'pe, 

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

 definite swallowing process, the soft mouth region widening into 

 a huge opening to receive the prey. Thus Dldiniiim nasutum 

 ordinarily swims about with little evidence of a mouth at the 

 extremity of the conical proboscis (Fig. 88, C), 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 Didininm 

 being reduced to a thin en\eloping sheath about the Paramecium 

 (Fig. 89). Similar, but not so spectacular c>i;ostomes are present 

 in other types of Gymnostomina. Spathidium spathida may 

 swallow smaller ciliates like Colpidium (Fig. 90), Nassula aurea, 

 Chilodon cucuUulns, etc., still smaller forms (Fig. 88, p. 179). 

 The Trichostomina are always provided with food-getting motile 

 organs and a constant stream of water with suspended bacteria 

 and other minute li\ing things passes through the permanently 

 open mouths making these creatures, according to jNIaupas, gluttons 

 par excellence of the animal kingdom. 



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 teres 

 or Spathidmm spathvla (Fig. 89, p. 180). In all of these cases there 

 is an armature of elongated rods, called trichites, formed of stereo- 

 plasmic substances, emliedded in the walls of the mouth and gidlet, 

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

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



