Luminosity and its Origin in a South African Earthworm. 209 
fatty nature, as they stain with osmic acid and Sudan III. But, though 
there seems now to be a general agreement that the chloragogen cells con- 
tain only excretory matter, the presence of fat has been detected in those of 
some Limicola, especially the family of the Enchytraeidae (Eosa, Freud- 
weiler). Willem has found fat globules in the chlorogogen cells of Are7iicola, 
and Ashworth in those of the Polychaete Halla. 
If these particles be of the nature of fat, the luminescence is sufficiently 
explained, as being merely a process of oxidation, as it is known that some 
substances of this nature react in this way.* As further evidence that the 
luminosity is caused by oxidation, I may mention that a quantity of the 
fluid, left on a slide under a cover-glass for a few days, was observed to give 
out light on removal of the cover-glass and exposure to the air. In one case 
the fresh material had been observed under a cover-glass ringed with vaseline 
to exclude air ; after examination the slide was put aside, and, about a month 
afterwards, on removing the cover-glass to clean the slide, the fluid was 
observed to be distinctly luminous, both on slide and cover-glass. Another 
slide of the same kind was kept about two months, but gave out no light 
when the cover-glas& was removed. It would thus appear that a slow pro- 
cess of oxidation takes place, during which no visible light is given ofl. 
Further evidence of this is that if the fluid be dried on the slide, and left 
for a few hours exposed to the air, it does not become luminous on the 
application of water or moisture. It may be noted also that if the luminous 
fluid be rubbed on a cloth or other substance the luminosity is increased, but 
dies down quickly. 
The test for luciferin and luciferase was applied, but these substances 
are apparently not present. 
Origin of the Luminous Cells. 
The cells, laden with inclusions of various sizes, might be the cells given 
off from some tissue of the earthworm itself, or cells of some parasitic proto- 
zoon undergoing rapid multiplication. They resemble most the free cells 
found in the body cavity of the earthworm, either chloragogen cells, or 
amoebocytes, laden with excretory matter ; but such cells are not known to 
find access to the digestive tract, though it may be noted that at first they 
were believed to form digestive ferments (D'Udekem) — a supposition which 
was abandoned when it was recognised that it was " impossible that the 
contents of the chloragogen cells could be poured into the lumen of the 
alimentary tract" (Burian). 
This being so, it was apparently impossible that the cells discharged 
from the mouth could be cells from the body cavity. It was therefore con- 
jectured that they were some stage in the life-history of a protozoon para- 
* E. Newton Harvey, " Studies in Biolumiscence," ' American Journal of Physio- 
logy/ vol. xli, No. 4, 1916. 
