240 Protoplasmic Dynamics. [ April, 
on the opposite side. And thus by breathing on one side and 
then on the other the vibration back and forth may be produced 
several times. Of course, in actual cilia the conditions are very 
different, for the material to be imbibed is ever present, while the 
imbibitional attraction is alternately freed first on one side and 
then on the other apparently by a chemico-electric, electro-motor 
process. And those who think it necessary to suppose a vital 
force here must be reminded that, according to Engelmann (op. 
cit. pp. 463-4), weeks after death, on stinking, decaying mem- 
branes, the cilia can be set in action by adding their normal con- 
ditions of oxygen, water and temperature. 
4. Zonate expansion with axial contraction, in a monomeric form 
pertains especially to such retractile parts as pseudopods, some 
cilia, and unstriated muscle cells, from imbibition in a zone of the 
conical or cylindriform part. The engorgement of this zone causes 
an influx into it shortening the long axis and tending to yield a 
spheroid form. In this way muscle cells 
and pseudopods broaden and shorten 
themselves, the latter sometimes to such 
an extent as to attain the diameter of the 
main mass, into which they thus merge. 
In the diagrams the light parts represent 
the expanding zones. With the poly- 
meric form of the striated muscle cells, 
. undulatory outlines result from the swell- 
ing of many successive zones giving 
greater and quicker contraction than in 
the smooth spindle cells. In this connection it must be borne in 
mind that a muscle’s action is only a resultant of the joint action 
of all its cells and that.attraction is the vs æ tergo of organic ex- 
pansion and contraction. 
5. Contra-actional retraction we can presume as the reverse of 
the exsertive, its center of imbibition being at the base of the 
pseudopod which becomes drawn to it. 
6. Spherogenic ballancement would occur from equal expansion 
-in all directions and cause the mass to assume a spherical form. 
VII.—The processes described above produce all the mass- 
motions of organisms, which are of a kinds and may be chiefly — 
grouped as: 
i Locomotive, for transporting individuals from m to SF o 
