io8 PARAMCECIUM, STYLONYCHIA, AND OXYTRICHA 



The protoplasm thus enclosed by the cuticle is distinctly 

 divisible into two portions an external somewhat dense layer, 

 the cortical layer or cortex (corf], and an internal more fluid 

 material, the medullary substance or medulla (med}. It will be 

 remembered that a somewhat similar distinction of the 

 protoplasm into two layers is exhibited by Amoeba (p. 3), the 

 ectosarc being distinguished from the endosarc simply by 

 the absence of granules. In Paramcecium the distinction is 

 a far more fundamental one : the cortex is radially striated 

 and is comparatively firm and dense, while the medulla is 

 granular and semi-fluid, as may be seen from the fact that 

 food particles (f. vac, see below, p. no,) move freely in it, 

 whereas they never pass into the cortex. It has recently been 

 found that the medulla has a reticular structure similar to 

 that of the protoplasm of the ordinary animal cell (Fig. 9, 

 p. 62), consisting of a delicate granular network the meshes 

 of which are filled with a transparent material. In the 

 cortex the meshes of the network are closer, and so form a 

 comparatively dense substance. The cortex also exhibits 

 a superficial oblique striation, forming what is called the 

 my op h an layer. 



The mouth (mth) leads into a short funnel-like tube, the 

 gullet (#/), which is lined by cuticle and passes through the 

 cortex to end in the soft medulla, thus making a free com- 

 munication between the latter and the external water. 



The cilia with which the body is covered are of approxi- 

 mately equal size, quite short in relation to the entire 

 animal, and arranged in longitudinal rows over the whole 

 outer surface. They consist of prolongations of the cortex, 

 and each passes through a minute perforation in the cuticle. 

 They are in constant rhythmical movement, and are thereby 

 distinguished from the flagella of Haematococcus, Euglena, 

 &c., which exhibit more or less intermittent lashing move- 



