62 



PROTOZOOLOGY 



in many Phytomastigina and Rhizomastigina, and a flagellum and 

 cilia are present in Ileonema (Fig. 273, b, c). 



In the cytosome of Protozoa there occur various organellae, each 

 of which will be considered briefly here. 



Fibrillar structures 



One of the fundamental characteristics of the protoplasm is its 

 contractility. If a fully expanded Amoeba proteus is subjected to a 



mc 









i*^:*/ 



^^- bg 



f:! glS 



Fig. 14. Myonemes in Stentor coeruleus (Schroder), a, cross-section of 

 ectoplasm; b, surface view of three myonemes; c, two isolated myonemes; 

 bg, basal granules; cl, cilium; gis, granules between striae; m, myonemes; 

 mc, myoneme canal. 



mechanical pressure, it retracts its pseudopodia and contracts into a 

 more or less spherical form. In this response there is no special or- 

 ganella, and the whole body reacts. But in certain other Protozoa, 

 there are special organellae of contraction. Many Ciliophora are able 

 to contract instantaneously when subjected to mechanical pressure, 

 as will easily be noticed by following the movement of Stentor, 

 Spirostomum, Trachelocerca, Vorticella, etc., under a dissecting 

 microscope. The earliest observer of the contractile elements of 



