PARAMECIUM 6l 



place, indicating that the protoplasm is of a fluid nature. The 

 ectoplasm (ec.) does not contain any of the large granules char- 

 acteristic of the endoplasm, since its density prevents their en- 

 trance. In this respect the two kinds of cytoplasm resemble 

 the ectoplasm and endoplasm of Ameba. Outside of the ecto- 

 plasm is a delicate elastic membrane, the pellicle (p.) or cuticle. 

 If a drop or two of 35 per cent alcohol is added to a drop of 

 water containing Paramecia, the pellicle will be raised in some 

 specimens in the form of a blister. Under the higher powers of 

 the microscope the pellicle is then seen to be made up of a great 

 number of hexagonal areas produced by striations on the surface 

 (Fig. 24, A). These striations are really very fine grooves (Fig. 

 24, B), which cross one another obliquely. 



The distribution of the motile organs, the cilia, corresponds 

 to the arrangement of the striations on the cuticle, since one 

 cilium projects from the center of each hexagonal area (Fig. 24, 

 A). These thread-like structures occur on all parts of the body, 

 those at the posterior end being slightly longer than elsewhere 

 (Fig. 23). A cilium may be compared to a very fine pseudo- 

 podium which has become a permanent structure. It is an out- 

 growth of the cell protoplasm, coming from a basal body called a 

 microsome (Fig. 24, B, B) which appears to arise from the nucleus. 

 The structure and movements of cilia have been studied by inves- 

 tigators for many years, and the following theories have been 

 proposed to explain them: (i) Cilia are somewhat stiff, lifeless 

 processes attached to the cell and moved by active elements 

 within the cell body (49). (2) Cilia are hollow elastic sheaths 

 into which a fluid is injected and withdrawn. (3) Cilia consist of 

 a complex fluid owing its contractility " to the presence of a 

 filament of kinetic granules, placed along one edge of the cilium, 

 the contraction of this thread furnishing the power of the cilium " 

 (52, p. 49). (4) Cilia are fibrillar, the movements being due to 

 the contraction of the fibrils. We are inclined to favor the last 

 theory, since the movements can only be adequately explained 

 by the presence of a contractile framework. Fibrils have been 



