PROTOZOA. 53 



seems to be against this view if we maintain that the 

 more elementary organisms came into existence first and 

 gave rise to the secondary or more complicated forms. 

 Surely one of the simplest representatives of the Flagel- 

 lata, the Monas termo, already described, is much more 

 specialized than the structureless, organless, ever-chang- 

 ing mass of protoplasm, the Protamoeba. 



INFUSORIA. 



The cilia or short hairs that clothe the cell of an Infu- 

 sorian, either partly or wholly, constitute one of the 

 important characters of this most specialized group of 

 Protozoa. We have seen that pseudopodia and flagella 

 can be converted the one into the other, but this is not 

 the case with pseudopodia and cilia. The latter have 

 become permanent and unchanging locomotive organs. 

 They move in unison after the fashion of paddles, while 

 the flagellum may be likened to a whip. 



One of the commonest Infusorians to be found in stag- 

 nant water and vegetable infusions is Paramoecium cauda- 

 tum Ehr. (PI. 54). Although of comparatively large 

 size, its rapid twisting motions make it difficult to observe 

 its many interesting specializations of structure. The 

 flagellum which we have seen so often in preceding forms 

 has disappeared, and the body of the Paramoecium is 

 provided with cilia which extend in longitudinal rows. 

 Here is found greater differentiation in the digestive sys- 

 tem, since the mouth which is at the bottom of the ciliated 

 depression (near the lower of the two outer arrows in the 

 left of the figure) leads into a tube that extends down- 

 ward a short distance. Food was given the Paramoecium 

 in the form of partly decomposed indigo obtained from 

 maceration of the leaves of the indigo plant, also carmine 

 from dried cochineal insects. The arrows on the left of 

 the drawing indicate the course of the particles of indigo 



