THE MASTIGOPHORA 127 



situated. The particles of food brought with the current find their 

 way into the body-plasm, where an indefinite cyclosis carries them 

 hither and thither until the digestible portions are separated from 

 the indigestible, and the latter are finally thrown out. James-Clark 

 ('66), Kent ('81), and most observers have maintained that, in the 

 Choanoflagellida, the food particles strike against the collar, subse- 

 quently working down on the inside to the mouth, but Entz ('83) and 

 France ('93, '97) claim that the mouth is not within the collar, but 

 that the so-called vacuole described by Biitschli ('84) is a soft ingest- 

 ing area at the base of the overlapping edge of the collar (see Fig. 69). 

 In Noctilitca, the flagellum brings a current of food toward the collar, 

 while the tentacle, which constantly beats down into the bottom of 

 the collar area, drives it into the mouth situated at the bottom of the 

 pharyngeal groove. The particles are then received into a gastric 

 vacuole, which, in the vicinity of the relatively large nucleus, per- 

 forms its function of digestion. 



E. VACUOLES 



Some of the vacuoles which make up the protoplasm of the Masti- 

 gophora are gastric, while others are contractile. The former are 

 formed about the food particles, which are probably digested in the 

 same way as in the Sarcodina, although in this group no experiments 

 have been made to test the digestive fluids. 



The contractile vacuoles, acting possibly as respiratory and excre- 

 tory organs, pulsate rhythmically and at definite rates, varying from 

 one or two pulsations per hour to five or six a minute, according 

 to the temperature and nature of the surrounding medium. They are 

 typically small, single or double in number (multiple in Chlorogonium}, 

 and are situated at either end of the body, or near the centre, while in 

 some cases they move with the granules in cyclosis. In some of the 

 more complicated types of Euglenidae, the vacuole is connected with 

 the so-called gullet by a minute canal. This canal in some cases 

 receives its supply of waste matter from a reservoir, which is the 

 receptacle for the contents of numerous small vacuoles surrounding 

 it, and which pulsate at regular intervals. 



F. REPRODUCTION 



Binary fission, the typical method of reproduction among the 

 Mastigophora, and the simplest of all modes of increase, is invariably 

 preceded by division of the nucleus. When chromatophores, eye- 

 spots, and pyrenoids are present, they also may be halved and 



