190 



ZOOLOGY 



Parasitic 

 Protozoa 



a time they coalesce to form a slimy wandering mass, 

 the plasmodium; and this, now living in the air, usually 

 on logs, forms a definite structure of characteristic ap- 

 pearance, which produces spores. The fructifying stage 

 usually incloses the spores, and is called a sporangium, 

 but in one group it has the spores on the outer surface 

 and is termed a sporophore. Some sporangia are very 

 large, that of Reticularia lye op er don Oycoperdon, a puff- 

 ball, which it resembles) is often 4 or 5 inches across. 

 The plasmodium or slime stage is a multinucleate mass 

 of protoplasm resulting from the union of a large num- 

 ber of cells, and as it grows the nuclei greatly increase 

 in number. It feeds on dead plant tissue. 



5. The Sporozoa (spore animals) are parasitic Pro- 

 tozoa, without cilia, but in certain genera producing 

 sexual forms, the male (sperm) cells then often flagel- 

 late. Reproduction is typically by spore formation 

 (compare the Mycetozoa), the individual breaking up to 



c 



Drawing by R. Weber 



FIG. 3g. Stages in the development of Didymium, one of the Mycetozoa (after 

 Lister) ; magnified about 1400 diameters. A, Spore. B, Swarm cell escaping from 

 a spore case. C, Swarm cell; /, flagellum. 



