454 University of California Publications in Zoology [Vol. 19 



noteworthy consequences. It is apparent, then, that the destruction of 

 the motorium or the severing of some or all of its attached fibers is 

 alone accountable for modifications in the perfect and efficient coordi- 

 nation between the series of membranelles and the anal cirri. We may, 

 therefore, regard these normal, morphological relationships as con- 

 ditioning the animal's usual behavior both in creeping and in 

 swimming. 



Previous to the researches of Sharp (1914) and Yocom (1918), 

 several other investigators had found fibers in certain ciliates, which 

 they believed to represent nervous elements. Engelmann (1880) 

 described distinct fibers associated with the peripheral and anal cirri 

 of Stylonyckia and concluded that they were nervous in function. 

 Neresheimer (1903) found two separate fibrillar systems in Stent or 

 coeruleus, one of which possessed muscular and the other nervous 

 properties. Their shape, size, selective staining, and relative positions 

 suggested these distinct functions. Moreover, this author found experi- 

 mental evidence supporting his interpretations. Lebedew (1908) 

 describes two systems of fibrils in Trachelocerca pJioenicopterus. On 

 one side and running parallel to each row of basal corpuscles appeared 

 a smooth, structureless fiber staining light, while another larger, less 

 even and densely staining fiber also ran parallel to the row of corpuscles 

 but on the opposite side. The latter was believed to be a myoneme and 

 the former was perhaps of nervous function. 



Other authors (Biitschli, 1889; Sehuberg, 1891; Schroder, 1906; 

 Maier, 1903; Prowazek, 1903; Griffin, 1910) have discredited the 

 "nerve hypothesis" for protozoans and have attributed to such systems 

 of fibers either the function of support or of contractility. 



It would seem that these discordant interpretations may owe their 

 origin largely to differences in the more general conception of the 

 nature of organization and degree of specialization anions the 

 Protozoa. And it is in the forming of this general conception that the 

 qualifying attributes — unicellular, primitive, and simple — assert them- 

 selves. In the light of the complex, embryogenic processes that give 

 rise to skeletal, muscular and neural tissues in the many-celled animals, 

 it is not easily conceivable how a single, undivided, simple and primi- 

 tive "cell" — the protozoan — could evolve organs performing these 

 specialized functions. Furthermore, it is evident that many protozoans 

 are similar in general appearance aDd in method of division to a 

 single metazoan cell; both are defined as "a mass of protoplasm con- 

 taining nuclear substance (chromatin) concentrated into one or more 



