LIFE HISTORY OF TWO RARE CILIATES 373 



by complete and speedy disintegration of the cell. This phe- 

 nomenon was observed on three occasions (figs. 45, 46). 



Von Erlanger's statement that he was able to trace the par- 

 tially retracted tentacles for a considerable distance inside the 

 body, I am unable to verify, as I have found no evidence of 

 the presence of these organs beyond the cortical region. Sec- 

 tions of Actinobolus show, scattered throughout the endoplasm, 

 many faintly staining threads, some very slender, others comma- 

 shaped, the head of the comma taking the nuclear stain more 

 intensely (figs. 62, 63, 64, 65). Although the threads closely 

 resemble the axial filaments of Camptonema pictured by Schau- 

 dinn, I have in no case found any connection between them and 

 the nuclear membrane. 



Maupas, looking upon the suctorian tentacle as a modified 

 pseudopodium, traced the origin of the ciliates from the rhizo- 

 pods through this group. Although bearing a resemblance to 

 the suctorian organs, the tentacles of Mesodinium, Ileonema 

 and Actinobolus differ radically from them in structure and 

 function, and, according to Biitschli, appear to be independent 

 modifications rather than organs of phylogenetic interest. 



The cilia, arranged in clusters of from five to ten at the base 

 of each tentacle, are long and show a flagella-like motion, rather 

 than the synchronous beating of ordinary cilia. 



At the posterior end of the body, situated somewhat eccen- 

 trically, is a large contractile vacuole, the pulsations of which 

 occur at intervals of one minute and a half. Once in some thir- 

 teen or fourteen beats a minute interval occurs.' Surrounding 

 the vacuole is a mass of minute dark granules, waste products 

 of metabolism. 



The mouth of Actinobolus does not open directly into the 

 endoplasm but is separated from it by a funnel-shaped gullet 

 described by both Entz and von Erlanger, although they do 

 not agree with respect to its structure. Entz noted the striated 

 walls of this organ and attributed the ridged appearance to the 

 presence of folds in the cortex, finding no evidence whatever 

 of solid rods; von Erlanger, on the contrary, interpreted the 

 ridges as distinct straight rods forming a weakly built basket. 



