172 



PROTOZOA 



covered by a membrane. The fine granules of the protoplasm usually 

 enter the pseudopodia and produce here, as they move back and forth, 

 the phenomenon of 'streaming.' Since foreign particles can participate in 

 this streaming, it follows that the movements depend on the protoplasm 

 itself. We have already used this fact (p. 55) to demonstrate the extraordi- 

 nary complexity of protoplasm. 



When Rhizopoda increase by division, the division products frequently 

 become flagellate spores or zoospores. The body becomes oval and 



develops, on the end which contains the nucleus, 

 one or more rlagella, which move more ener- 

 getically than pseudopodia, and are permanent 

 as long as the zoospore stage persists (fig. 122). 

 Since many Protozoa possess flagella along with 

 pseudopodia, the boundary between Rhizopods 

 and Flagellates is not distinct (fig. 119). 



The Rhizopoda form an ascending series in which 

 the systematic characters become more and more 

 pronounced; such are the assumption of a definite 

 form, as in the Radiolaria and Heliozoa, the forma- 

 tion of a skeleton of regular character, as in the 

 Thalamophora, or the development of a peculiar re- 

 production, as in the Mycetozoa. At the bottom 

 FIG. 1 19. Mastigamceba stand the Monera and the Lobosa whose characters 

 aspera (after F. E. Schulze). are mostly negative, for neither form, skeleton, nor 



reproduction affords systematic distinctions. 



Order I. Monera. 



The most important character of the Monera is the lack of a nucleus. As 

 with other negative characters this is somewhat uncertain. In many cases, 

 especially when the protoplasm is filled with pigment granules, the nucleus is 

 recognized with difficulty, and hence animals have been described as anucleate 

 in which the nucleus was overlooked. So it is possible that, in the few forms 

 now remaining in the group, the nucleus has merely escaped observation; 

 possibly it is functionally replaced by the chromidia (p. 58). There are several 

 theoretical reasons favoring the idea of anucleate organisms. It is easier to 

 suppose that with the appearance of life there were organisms consisting of but 

 a single substance than that these organisms had nucleus and protoplasm al- 

 ready differentiated. Several species of Protamccba are placed in the Monera. 



Order II. Lobosa (Amcebina). 



Lobosa are primitive Rhizopoda with one or several nuclei. The 

 species of Anuvba, forms which owe their name to their constant change 

 of shape, are typical (figs. 117, 120). This change of form is due to the 

 formation and disappearance of a few finger-like (lobose) pseudopodia. 

 Body and pseudopodia consist of two layers, a soft granular inner entosarc 

 (en) and a firmer, clear, outer ectosarc (ek). In the entosarc is usually 



