ACTIVITIES OF COLONIAL ANIMALS 493 
of the whitish chalky material and the peripheral part of the light 
yellowish substance. These two materials, however, were so 
intimately associated that it was found impossible either to sep- 
arate them satisfactorily or to determine by direct inspection 
which was responsible for the light. In only one region could 
satisfactory evidence be obtained and that was on the extreme 
edge of the rachis. Here the two materials form a well-marked 
double fringe, the outer fringe being composed of the white 
material and the inner one of the yellowish. This edge, espe- 
cially when observed from the ventral side of the rachis, shows 
these two fringes with great clearness, and when phosphorescence 
occurs, it can be definitely seen that the light is associated with 
the whitish substance and not with the yellowish one. Hence I 
conclude that the phosphorescence emanates from the white 
component of the light-colored masses. The light that this com- 
ponent produces when seen under a hand-lens is indescribably 
beautiful; it is a combination of intense blue-greens comparable 
to what one sees in a brightly illuminated opal. 
The application of mechanical or electrical stimuli under appro- 
priate conditions to the rachis of Renilla results in what seems to 
be a series of luminous waves emanating concentrically from the 
region of stimulation. When one of these wave fronts is closely 
scrutinized, it is found to be not a continuous line, but a series 
of luminous points which represent the small masses of white 
material already alluded to as the source of the light and which 
for the moment lie in what would be a continuous wave front. 
Thus the appearance of a wave is due to the momentary glowing 
of one concentric line of points after another as the impulse that 
induced the phosphorescence spreads from the center of stimu- 
lation outward. This spread of light from the center of stimu- 
lation to the rest of the colony in other sea-pens than Renilla was 
apparently first recorded by delle Chiaje in 1836 (Panceri 71, 
j)4 abl). 
' As with rachidial peristalsis, the waves of luminosity pass 
around incisions in the rachis, provided these incisions do not 
completely separate the parts concerned. If the rachis is cut 
nearly in two transversely, the luminous waves may be started 
