CILIARY MOVEMENT 33 



probably formed by the conversion of a thin superficial 

 layer of protoplasm into cellulose, the cyst attaining its final 

 thickness by frequent repetition of the process (see p. 14). 

 The starch of the pyrenoids is apparently formed by a similar 

 process of decomposition or destructive metabolism of pro- 

 toplasm, growth taking place in both instances by accretion 

 and not by intussusception. 



We see then that destructive metabolism may result in the 

 formation of (a) waste products and (b) plastic products, 

 the former being got rid of as of no further use, while 

 the latter remain an integral part of the organism. 



Let us now turn once more to the movements of Haemato- 

 coccus, and consider in some detail the manner of their 

 performance. 



Each flagellum (Fig. 3, A, fl) is a thread of protoplasm of 

 uniform diameter except at its distal or free end where it 

 tapers to a point. The lashing movements are brought 

 about by the flagellum bending successively in different 

 directions ; for instance, if in Fig. i F, abc represents it in 

 the position of rest, abc' will show the form assumed when 

 it is deflected to the left, and abc" when the bending is 

 towards the right. In the position abc the two sides ab, ac 

 are obviously equal to one another, but in the flexed 

 positions it is equally obvious that the concave sides ac', be" 

 are shorter than the convex sides be,' ac" in other words, as 

 the flagellum bends to the left side ac becomes shortened, 

 as it bends to the right the side be. 



This may be otherwise expressed by saying that, in bend- 

 ing to the left the side ac contracts (see p. 10), in bending to 

 the right the side be, or that the movement is performed 

 by the alternate contraction of opposite sides of the 

 flagellum. 



D 



