35' 



THE LOCOMOTION OF MICROSCOPIC AQUATIC 



ORGANISMS^ 



By D. J. Scourfield, F.Z.S., F.R.M.S. 



(A Resume of a Lecture delivered on December Wi, 1908.) 



Before considering the various special methods of locomotion 

 exhibited by microscopic aquatic organisms, a brief reference to 

 some of the general conditions of locomotion under water, and 

 the problems arising therefrom, will, I hope, make the subject 

 somewhat more interesting and at the same time serve to show 

 that the study of such matters is of wider significance than might 

 at first sight be supposed. 



At the outset it must be remembered, in regard to organisms 

 living in water, that the medium in which they are immersed 

 affords them very considerable support, not only for their bodies 

 as a whole, but for all their appendages and outgrowths if such 

 be present. This of course is due to the fact that the majority of 

 organisms are, in the main, made up of tissues having a specific 

 gravity differing very little from that of water, and the result is 

 that extremely delicate and jelly-like creatures can live without 

 difficulty in water. The most delicate and fragile of all known 

 organisms are, as a matter of fact, found in water. 



In consequence of this equable support and the comparatively 

 small amount of friction to be overcome, very little energy has to 

 be expended to produce slow movements, and if the organisms are 

 actually of the same specific gravity as water and can get their 

 nourishment directly from the substances dissolved therein, as 

 sometimes happens, it is not necessary for them to be provided 

 with swimming organs at all. They can then depend entirely 

 for change of position upon the never-ceasing movements, 

 due to various physical causes, taking place within the water 

 itself. 



As water, when compared with dry land, offers such a small 

 amount of resistance, it is at once apparent that for movement 



