492 G. H. PARKER 
When a glowing rachis is examined under a hand-lens the parts 
from which the light emanates are seen to be the accumulations 
of whitish material in which the siphonozodéids are imbedded and 
which surrounds the bases of the autozodids. Apparently light 
emanates from no other source. If the peduncle with the narrow 
smooth band of tissue leading from this body to the axial siphono- 
zooid is cut from a Renilla that is capable of phosphorescing, no 
amount of stimulation either mechanical or electrical will call 
forth any luminosity in it. No phosphorescence has even been 
induced on the ventral surface of the rachis. Phosphorescence 
is quite clearly limited to that part of the dorsal surface of the 
rachis that is covered by the zodids, and, as already stated, the 
particular bodies concerned with luminosity are the small accu- 
mulations of light-colored material limited to this region. The 
observations upon which this statement rests are not as easily 
and directly made as might be supposed. As the phosphores- 
cence of Renilla is best seen only in complete or almost complete 
darkness, it is impossible to determine at the time when the light 
can be seen the exact spot from which it emanates, for the 
light itself is not strong enough to illuminate the general surface 
of the rachis. An indirect method of determining the exact 
parts concerned in light production was therefore resorted to 
and the various parts of the rachis were tested. For instance, 
in a dim artificial light, a single autozodid was cut from a colony 
and placed upon a glass slide. This was then carried into a dark 
room, covered with another slide and crushed. Under such cir- 
cumstances no light was even observed. The same was true of 
fragments of the purple flesh of the dorsal surface of the rachis. 
When, however, a group of siphonozoéids with the surrounding 
light-colored material was crushed, a momentary sparkling could 
be clearly seen. This was also observed when the light-colored 
base of an autozodid was crushed. These two parts were the 
only parts from which light could be produced in Renilla. 
The light material which is thus associated with phosphores- 
cence is seen on close inspection to include two substances: a 
whitish chalky substance and a light-yellowish crystalline one. 
Thus in a group of siphonozoéids the central portion is made up 
