PROTOZOA. 47 



ments and found he was able to force the animal from a 

 Heliozoan to a flagellate condition by striking the sides 

 of the dish when, as if disturbed, the Dimorpha would 

 develop whips and swim quickly about. 



The flagellate Mastigophora are well represented by 

 the series of forms shown in PI. 51. The body of Monas 

 termo Ehr. ? (fig. i, x 950) is occasionally somewhat 

 amoeboid, sending out short pseudopodia-like continua- 

 tions. It is a free-swimming animal but may become 

 fastened temporarily by a thread-like prolongation of the 

 posterior end of the body (fig. 2, x 1200). At the for- 

 ward end is the whip or flagellum, and on one side of its 

 base is the beak-like prominence or lip. Between this lip 

 and the base of the flagellum is the mouth, which, how- 

 ever, does not extend into an oesophagus. The flagellum 

 catches the food and it is thrown with a sudden jerk 

 directly against the mouth. "If acceptable for food the 

 flagellum presses its base down upon the morsel, and at 

 the same time the lip is thrown back so as to disclose the 

 mouth, and then bent over the particle as it sinks into 

 the latter. When the lip has obtained a fair hold upon 

 the food, the flagellum withdraws from its incumbent 

 position, and returns to its former rigid, watchful condi- 

 tion. The process of deglutition is then carried on by 

 the help of the lip alone, which expands laterally until it 

 completely overlies the particle. All this is done quite 

 rapidly, in a few seconds; and then the food glides 

 quickly into the depths of the body, and is enveloped in 

 a digestive vacuole, whilst the lip assumes its usual coni- 

 cal shape and proportions." We have quoted the above 

 from Prof. H. James-Clark 1 to show the specialization in 

 structure which characterizes this animnl. In none of 

 the Protozoa already described have we found an appara- 

 tus for forcing food into the body at one particular place. 

 If this process were long continued, it is not difficult to 



1 Mem. Boston Soc. Nat. Hist., I, 1866, p. 307. 



