lOS BIOLOGY OF THE PROTOZOA 



some cases, however, especially in parasitic ciliates like Ophri/oscolex 

 or Diplodinmm eraiirJafvui, there is a specialized differentiation of 

 the "cuticle" discovered by (xunther and well described by Sharp. 

 These peculiar differentiations function according to the latter 

 observer, as endoskeletal structures for the attachment of conspic- 

 uous band-form myonemes, which serve as retractor strands for 

 drawing into the body a characteristic gullet and adjacent organ- 

 oids (Fig. 2, p. 20). These skeletal elements are formed from the 

 ectoplasm and are hardened, according to Eberlein, by a deposit 

 of silicic acid which, as Sharp implies, may be the explanation of 

 their rigid but brittle nature. 



Myonemes or analogous organoids are not confined to the ciliates 

 but may be found in some types of Gregarinifla and in one group 

 of the Radiolaria. The so-called myonemes of the Tr\'panosoma- 

 tidse, however, are very dou})tful kinetic elements but, more prob- 

 ably, are analogous to the cuticular markings which are frequently 

 found on the periplast of flagellates. In some of the gregarines, 

 myonemes form a thick layer of extremely fine fibrils in the contrac- 

 tile zone of the ectoplasm, running circularly, or possibly spirally, 

 about the cell, their contractions giving rise to the peristaltic move- 

 ment so characteristic of these forms. 



Myophrisks of the Radiolaria are contractile strands which are 

 fastened by their distal ends to the extremities of the axial bars of 

 the Acantharia. The proximal ends fray out into fibrils which are 

 lost in the reticulum of the gelatinous mantle or calymma, of the 

 ectoplasm. By their contractions the cal\mma is drawn up to the 

 ends of the axial bars whereby the diameter of the organism is in- 

 creased and its specific gravity decreased, the reverse occurring 

 with their relaxation. The myonemes thus seem to play a part in 

 the hydrostatic activities of these Radiolaria although this func- 

 tion is difficult to understand since the change in sj^ecific gravity 

 is usually interpreted as a means by which these motionless forms 

 escape from adverse conditions on the surface. We should expect, 

 however, that rough water or other surface conditions deterimental 

 to the organisms, would be sources of stimulation which should cause 

 the contractile elements to contract and thus to defeat their appar- 

 ent purpose by decreasing the specific gravity'. 



Cudrdinating Fibers.— If a single cilium of a resting Pleuronema 

 be touched the entire organism responds. Here and in similar cases 

 there appears to be a definite tactile function. In flagellates also 

 it is not improbable that certain flagella, as the anterior flagella of 

 Caduceia theobromcB described hy P'ran9a (1918), or indeed possibly 

 all flagella have a more or less well-developed sensory function. 

 In ciliates, such as Paramecium caiidaiinn, with a uniform coating 

 of cilia, the motile elements do not all beat simultaneously, but a 

 wave of contraction, beginning at the anterior end, passes down the 



