12 Elementary Zoology. 



the myophan layer, concentrated in the stalk to form the muscle 

 fibre j while instead of pseudopodia, appearing when and where 

 they are wanted, are definite and persistent outgrowths of the 

 ectosarc, which have the power of independent movement. 

 Yet there is not so wide a difference as might be thought be- 

 tween the heavy, slowly flowing, pseudopodia and the actively 

 vibratile cilia. Some amoebse have very slender pseudo- 

 podia, while organisms belong to the protozoa have long 

 thin fixed processes, from which to cilia is not a long step. 

 Approaching the matter from the other side, cilia have 

 been observed in the living animal to " melt down " into 

 pseudopodia. 



The vorticella multiplies by division, and also after what 

 may be termed a sexual union. A bell divides down the 

 middle, and two vorticellse are the result. This division results 

 in the production of two kinds of individuals ; one is like 

 the parent form, the other is a locomotive body with a ring of 

 cilia at each end of the body. The locomotive body, after a 

 longer or shorter interval, settles down and becomes a stalked 

 vorticella?- Or one of these locomotive individuals will attach 

 itself to a stalked bell, and become fused with it, the nuclei 

 becoming broken up, fusing with those of the other individual, 

 ultimately reacquiring their original form. Ordinary division 

 occurs after this which may be compared to a sexual process. 

 It has been shown that, after a certain number of generations 

 produced by simple division there is a need for this sexual 

 union to restore the exhausted protoplasm. 



' Soraelimes, particularly if the water be too foul, a vorticella will 

 detach itself from its stalk and lead a free existence, forming later a new 

 stalk , and settling down to a sedentary life. 



