584 Journal of the Asiatic Soc. of Bengal. [N.S., XVIII, 1922.] 
motion and heat or of motion and electricity in other animals. 
In warmer regions the light appears as a strong glow or a flash 
for a second or so after mechanical stimulation, while in 
colder waters the light is strong and appears as a steady glow 
lasting for a minute or more. The light is localised in the 
region of the swimming plates, and the production of light is 
at its maximum at the optimium temperature at which the 
animals usually live; direct sunlight, however. inhibits lumino- 
sity, while mechanical stimulation accelerates the power to 
light. The light, as has been noted already, is produced in the 
region of the swimming plates only, and it has been estab- 
lished by histological investigations, that it is probably pro- 
duced in special cells. Underneath the swimming plates are 
the water vascular canals, and linning these canals are the 
genital cells; lying distally to the genital cells are rows of 
arge vacuolated cells. It is most probably in these cells that 
luciferine is secreted, and stored in the vacuoles. The lucifer- 
ine produces light by its combustion. Curiously, however, 
the secretion of luciferine is not begun till the animals have 
been kept in darkness for some time or are brought into dark- 
ness, while combustion does not start till some stimulus of a 
mechanical nature is applied. It may also be noted that the 
combustion is of an intra-cellular nature. 
Coming now to my observations on these two forms, it 
as those summarised above. No light was observed in pieces 
without the ciliated swimming plates, but in others, where 
even a small part of the plate was intact, a faint glow, lasting 
for half a second to a second, was observable at irregular inter- 
vals. In freshly captured specimens stimulation resulted in 
the production of light at more regular and shorter intervals. 
For stimulation gentle shaking of the water was quite enough. 
summing up the observations it may be noted that in 
the case of the animals observed in the Delta, true light-pro- 
ducing organs were found only in the two Ctenophores and 
that in the fish and prawn, which showed phosphorescence, 
the phenomenon was due to light-producing Bacteria. 
