ACINETARIA 



75 



form a kind of cup enclosing and protecting the greater part of the 

 body of the creature. In the endoplasm are the nuclear apparatus 

 (macro- and micronucleus) and contractile vacuole as in ordinary 

 Ciliates. 



In the sedentary Acinetarian the cilia have disappeared but there 

 are present other projections of the protoplasm which constitute its most 

 characteristic feature : these are the sucking tubes. Each of these^ 

 which looks like an extremely slender pin projecting from the body, 

 is really a very fine straight tube with a slightly expanded trumpet- 

 shaped end (Fig. 30, t). The wall of the tube is a prolongation of the 

 stiff ectoplasm while the interior contains fluid. The tubes vary in 



B 



Fig. 30. 



Acinetaria. A, Tokop/irya ; B, Acineta, showing young ciliated stage, c.y, Contractile vacuole ; 

 embt embryo ; N, macronucleus ; n, micronucleus ; /, suctorial tube. 



number in different Acinetarians from one up to a large number, when 

 many are present they may be either scattered irregularly or as in the 

 genus Acineta collected into clumps. 



The function of the sucking tubes is seen if a small Ciliate knocks up 

 against them. It adheres to the end of the tube and its protoplasm is 

 gradually sucked down through the tube into the endoplasm of the 

 Acinetarian where a food-vacuole forms round it and it is gradually 



digested. 



That the conclusion which may be drawn from the presence of the 

 characteristic Ciliate type of nucleus that the Acinetaria are modified 

 Ciliates is correct is shown by the study of their life-history — for the 

 young stage is provided with cilia and swims about like an ordinary 

 Ciliate. The young creature arises as a kind of bud, as a projecting piece 



