MOVEMENT 



Numbers of the unicellulars alter their position very 

 characteristically by secreting a thick mucus at one side 

 of their body and fastening this to the ground. If the 

 secretion continues, a longish jelly-like stalk is produced 

 by which the cell slowly pushes itself along, like a boat 

 with a rowing-pole. This secretory locomotion is found, 

 among the protophyta, in the desmidiacea and diatomes, 

 and in some of the gregarinae and rhizopods among the 

 protozoa. The peculiar rolling movements of the os- 

 cillaria (threadlike chains of blueish-green unnucleated 

 cells, closely related to the chromacea) are also effected 

 by the secretion of mucus. On the other hand, it is 

 probable that the sliding movements of many of the 

 diatomes are due to fine processes (vibratory hairs?) in 

 the plasm, which proceed either out of the seams (raphe) 

 of the bivalvular silicious shells or through the fine pores 

 in them. 



Especially important in the easy and rapid locomotion 

 of many unicellulars is the formation of fine hairlike 

 processes at the surface of the body; in the broadest 

 sense, they are called vibratory hairs. If only a few 

 whiplike threads are formed, they are called whips 

 (flagella); if many short ones, lashes (cilia). Flagelli- 

 form movement is found in some of the bacteria, but 

 especially in the mastigophorous "whip-infusoria," in 

 the mastigota among the protophyta, and the flagellata 

 among the protozoa. As a rule, we have in these cases 

 one or two (rarely more) long and very thin whip- 

 shaped processes, starting from one pole of the long axis 

 of the oval, round, or long cell-body. These whips 

 (flagella) are set in vibratory motion (apparently often 

 voluntary) in various ways, and serve not only for swim- 

 ming or creeping, but also for feeling and securing food. 

 Similar whip-cells (cclluhc flagcllatcc) are also found very 

 commonly in the body of tissue-animals, usually packed 

 together in an extensive layer at the inner or outer sur- 



271 



