GROWTH AND MOVEMENT 
445 
are often included in the animal kingdom (see p. i). The plasmodium 
is a naked mass of protoplasm (sometimes like a thin cake, often a richly 
anastomosed network), which during its vegetative period lives in wet 
places among decaying wood, leaves, etc. The creeping is accomplished 
by the protrusion of marginal lobes of the protoplast along one side, and 
toward these the rest slowly flows. In this way the whole mass advances 
in a definite direction, which is frequently changed and is subject to 
control by external agents. Thus, by varying the temperature, the mois- 
ture, or the illumination, the plasmodium may be made to creep in one 
direction or another. Its response to these stimuli, however, differs 
with its own stage of development. Whereas during a considerable 
vegetative period it avoids light and drier places, later it creeps out from 
the substratum and ascends to drier and exposed situations, where it 
produces sporangia with a casing and framework of cellulose and a 
multitude of spores. 
Excretory movements. Excretory movements are executed by some 
diatoms and desmids, and those of Oscillatoria and Spirogyra are 
probably of this sort. The diatoms and desmids forcibly excrete muci- 
lage through slits or pores in the wall against the substratum (a glass slide, 
the wall of an aquarium, the bottom of a pool, or the surface of a water 
plant) over which they creep slowly with a majestic 
and mysterious motion, which is not yet fully under- 
stood (see also p. 451). 
Ciliary movement. The more rapid movements 
are called ciliary, because executed by the lashing of 
slender threads of protoplasm through the water, in 
which alone such organisms can move. The motile 
threads are known as cilia or flagella. 1 They arise 
from different places on the protoplast, often at the 
pointed apex or along a band, where the special 
organ which produces them, the blepharoplast, is 
located (fig. 678). The flagellates (unicellular organ- 
isms of uncertain relationship, p. 20), bacteria, the 
zoospores and gametes of certain algae and fungi, 
and the sperms of bryophytes, pteridophytes, and 
FIG. 678. Swarm 
spore of Hydrodictyon, 
with two cilia arising 
from a blepharoplast 
with nuclear connec- 
tions. After TIMBER- 
LAKE. 
1 No constant distinction can be made between cilia, which are typically short, hair- 
like, and numerous, and flagella, which are long, whiplike, and few (1-4) for each cell. 
Yet a cell sometimes has a single cilium, or two, and flagella are numerous on the sperms 
of ferns. 
