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 gregarinæ and rhizopods among the protozoa. The peculiar rolling movements of the oscillaria (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_). Flagelliform 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 swimming or creeping, but also for feeling and securing food. Similar whip-cells (_cellulæ flagellatæ_) are also found very commonly in the body of tissue-animals, usually packed together in an extensive layer at the inner or outer surface (ciliated epithelium). If single cells are released from the group, they may live independently for some time, continuing their movements and resembling free infusoria. The same may be said of the travelling spores of many of the algæ, and of the most remarkable of all ciliated cells--the spermia or spermatozoa of plants and animals.