240 



THE PROTOZOA 



FIG. 98. Flagellula of 

 Stemonitis fusca, show- 

 ing successive stages in 

 the capture of a bacillus. 

 In a it is captured by 

 one of the pseudopodia 

 at the hinder end ; in c 

 it is enclosed in a diges- 

 tive vacuole. Another 

 bacillus is contained in 

 an anterior vacuole. 

 From Lister, magnified 

 800. 



be several inches across and contain many thousands of nuclei. 



The plasmodium moves about in various directions, showing 

 exquisite streaming movements of the proto- 

 plasmic body (Fig. 99). The nature of the 

 food varies in different species ; the majority 

 feed on dead vegetable matter, but some 

 attack and devour living fungi. The mode 

 of nutrition is generally holozoic, but in 

 some cases perhaps saprophytic . Contractile 

 vacuoles are present in large numbers in 

 the protoplasm, in addition to the innumer- 

 able nuclei, which are all similar and not 

 differentiated in any way. The plasmodia 

 are often brightly coloured. 



From their mode of life, the plasmodia 

 are naturally liable to desiccation, and when 

 this occurs the plasmodium passes into the 

 sclerotial condition, in which the proto- 

 plasm breaks up into numerous cysts, each 

 containing ten to twenty nuclei. When 

 moistened, the .cysts germinate, the con- 

 tained masses of protoplasm fuse together, 



and so reconstitute the active plasmodium again. 



The plasmodium represents the trophic, vegetative phase, which 



is succeeded by the reproductive phase, apparently in response to 



external conditions, such 



as drought, but more es- 

 pecially scarcity of food. 



The reproduction begins 



by the plasmodium be- 

 coming concentrated at 



one or more spots, where 



the protoplasm aggre- 

 gates and grows up 



into a lobe or eminence, 



the beginning of the 



sporangium (Fig. 100), 



the capsule in which the 



spores are found. The 



sporangium is modelled, 



as it were, on the soft 



protoplasmic body, and 



takes the form of a 



rounded capsule, attached to the substratum by a disc-like 



attachment known as the hypothallus. Between the sporangium 



FIG. 99. Part of a plasmodium of Badhamia 

 utricularis expanded over a slide. From 

 Lister, magnified 8 diameters. 



