DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 135 



the silver line system and, according to Bresslau, Kah'l and others, 

 are here represented by grannies when the trichocysts are undevel- 

 oped. In such granular form they are sometimes called "pro- 

 triehocysts" and Bresslau regards them as the source of the "tektin" 

 which forms artificially produced tests and houses (see p. 137). 

 The trichites are stiff, usually rod-like supporting structures and are 

 rarely discharged. 



n. DIFFERENTIATIONS OF THE CORTEX. 



It is quite probable that there is no such thing as an entirely 

 naked cell among the Protozoa. Even in Amoeba proteus, the class- 

 ical example of a naked cell, the ectoplasm is covered by a delicate, 

 viscous hyaline zone of modified protoplasm. Hofer, Verworn, 

 and others, have noted it in connection with food taking; Schaeffer 

 (1917), in connection with movement claiming that it is a third 

 kind of protoplasm in addition to ectoplasm and endoplasm and 

 Chambers (1915) came across it in connection with micro-dissection 

 experiments. Among Sporozoa and Infusoria it has been described 

 in many species, and in flagellates and ciliates it is not infrequently 

 characterized by definite markings or sculpturing. It is the most 

 external portion of the cell and is distinguished from the remainder 

 of the cortex by the special name periplast or pellicle. 



The periplast always fits the body closely, dividing when the 

 body divides. In Paramecium caudatum during plasmolysis it is 

 extremely delicate, but may be seen when it becomes separated 

 from the rest of the cortex and distended by the accumulation of 

 fluids. In other cases it is much more definite and membrane-like 

 as in Cochliopodium bilimbosum (Fig. 9, p. 31), or in the loricate 

 ciliates such as Euplotes harpa, Uronychia setigera and their allies. 

 Periplasts are frequently delicate enough to give way to forces 

 generated within the body, but elastic enough not to break, a phe- 

 nomenon resulting in peristaltic movement which is not infrequent 

 in Gregarinida (e. g., Monocysti* agilis) and in some flagellates. 

 Such organisms are said to be "metabolic" and the peculiar motion 

 is sometimes called "euglenoid movement." 



In many cases the periplast is ornamented by striations which 

 usually run obliquely down the cell; in some cases by ridges; by 

 furrows or by nodules as in the ciliate Vorticella monilata. In 

 Coleps hirtus the periplast is differentiated into definite plates of 

 characteristic form arranged in four girdles which compose an 

 armature for the organism (Fig. 73, A, C). The skeletal structures 

 of endoparasitic ciliates, e. g., Diplodinium ecaudatum are likewise 

 differentiations of the periplast (p. 21). 



Not only the periplast, but the entire cortex has become differen- 

 tiated in a great variety of ways in response, apparently, to the 



