306 THE ZOOLOGIST. 



trailed behind during progression, and serving apparently as an 

 assistant in the process of feeding ; I have also seen it used, in 

 -one species, as an anchor, a sticky secretion being apparently 

 produced which fastens its tip to any solid object handy. Finally, 

 -the groups Tetramitina, Polymastigina, and Trepomonadina, which 

 lead up to the peritrichous Ciliata, have from three to eight 

 flagella, terminal and lateral, while the remarkable connecting 

 form Lophomonas (which we shall meet again later on) has a 

 bunch of about two dozen at its anterior pole. 



Here, again, selection has some material to work upon. It 

 -cannot be denied that two flagella are better than one when, as 

 often occurs, they give their possessor the power of more rapid 

 and powerful movement, and so enable it to more quickly remove 

 itself from danger ; the value of such powers to a small organism 

 is quickly realised by anyone who watches a Paramecium feeding. 

 Again, two flagella may make a better vortex than one, and are 

 hence more efficient for the collection of food. 



Nevertheless, the theory which bases the multiplication of 

 the flagella on the action of natural selection breaks down on 

 closer scrutiny. If natural selection has been the cause of the 

 development of poly-flagellate forms, then either the mono- 

 flagellates must be adapted to different conditions of life than 

 those of the former group, or else the latter less efficient forms 

 must have become extinct or nearly so. Neither statement fits 

 the facts. The conditions of life are precisely similar in both 

 (highly-aberrant forms like Eitglena excepted). In both cases 

 the food-supply consists of bacteria and particles of dead organic 

 matter ; both types are found in every conceivable environment, 

 from a horse-pond to a rain-barrel ; there is no difference what- 

 ever. As to the second eventuality, no disproof of its non- 

 fulfilment is needed. 



Indeed, it does not seem that even the premises of the argument 

 for selection are valid. 11; is true that the general preponderance 

 of activity is on the side of the poly-flagellates and that many 

 mono-flagellates are very large compared to others of the former 

 group (not that their size is sufficient to be of much survival-value 

 in competition with the much larger ciliates or with the Heliozoa 

 or Tentaculifera) . But many small mono-flagellates are as active 

 as their relatives with more flagella than one ; while others of 



