Marine Snails — HANEDA 
155 
tensity became progressively weaker after 30° 
C., despite an increase of temperature to 60° 
C. At this point the intensity had dropped to 
zero, and during the following decrease in 
temperature, it showed no discernible recov- 
ery. As far as could be determined, the snails 
had died at approximately 60° C. 
STRUCTURE OF THE LUMINOUS ORGAN 
IN Planaxis labiosus 
The luminous organ, situated on the dorsal 
part of the mantle in the limited area shown 
in Figure 3, is a translucent pale blue color 
when fresh. The external visible area of this 
luminous organ consists of many folds of 
luminous tissues which run parallel with each 
other. If the body is taken out of the shell 
and put into an aluminum morine solution 
(diluted 500,000 times) for a few minutes and 
then washed carefully in fresh water, it is 
possible, by observation with Yasaki’s fluo- 
rescent microscope (1952), to see the beautiful 
Fig. 3. Dorsal view of the body of Planaxis labiosus , 
removed from the shell. I, Luminous area of mantle; 
m, mantle; col , collar; p, propodium; t, tentacles. 
Fig. 4. Effect of temperature on Planaxis labiosus 
luminescence. (Numbers on the vertical axis are counts 
of the recorder of the photomultiplier.) 
blue-green fluorescent light which these lu- 
minous tissues emit. The structure of all five 
luminous species of Planaxis is practically the 
same: the luminous cells are restricted to this 
area of the mantle. 
HISTOLOGY 
Since the luminescence of this snail is lo- 
calized in a limited area on the mantle and the 
animal is small in size, the whole body was 
preserved in a fixative of sea water prepared 
with formalin and Bouin’s solution. The ma- 
terial was cut in 10 n sections both longi- 
tudinally and transversely. The stains used 
were haematoxylineosin and aluminum mor- 
ine. The appearance of the longitudinal sec- 
tion of the mantle is much like that of a comb. 
On the inside of the mantle, where the lumi- 
nous area is situated, there appeared many 
pleats arranged in parallel, but it was impos- 
sible to determine whether or not these pleats 
contain luminous cells. However in the lu- 
minous area of the mantle, under the thin 
epithelium, there appeared many cellular 
masses, which very probably contain the 
photogenic tissues of this body. Each of these 
masses consists of small, closely packed cells. 
