154 
PACIFIC SCIENCE, Vol. XII, April, 1958 
TABLE 1 
Date and Place of Collection of the Various Species of the Genus Planaxis and 
Their Size and Remarks 
SPECIES 
n att 
SIZE OF SHELL 
REMARKS 
U A I 
Height, 
mm. 
Diameter, 
mm. 
Planaxis virgatus Smith . . . 
Borawazawa Beach, Ha- 
chijo I., Japan 
Habu, Ohshima I., Japan 
April, 1953 
Oct. 1953 
8.0 
4.0 
Luminous 
P. periscelida Dali 
Heta, Izu Peninsula, Japan 
May, 1953 
3.5 
2.0 
Luminous 
P. longispira Smith 
Dogashima, Izu Peninsula 
Japan 
Aug., 1953 
6.0 
2.8 
Luminous 
P. lineatus da Costa 
Waikiki Beach, Honolulu, 
Hawaii 
March, 1954 
10.0 
5.2 
Luminous 
P. labiosus A. Adams .... 
P. labiosus A. Adams .... 
Onekahakaha Beach, Hilo, 
Hawaii 
Key West, Florida 
March, 1954 
April, 1954 
10.0 
5.0 
Luminous 
P. sulcatus Born 
Shirahama, Wakayama 
Pref., Japan 
April, 1955 
15.0 
10.0 
Non-luminous 
appears once again. After crushing the shell 
and removing the body of the snail, a low 
power magnification will show that the lumi- 
nous part of its body is situated on the mantle 
in a limited area (Fig. 3) . When the body is put 
into fresh water, the light on the mantle con- 
tinues as a more prolonged glow. However, 
after 10 or 15 minutes in fresh water, the 
animal becomes weak and its light cannot be 
seen even after strong stimulation. If the body 
is placed on photographic film for a few min- 
utes in the dark, an image of the light appears. 
Observed under the microscope in the dark, 
the luminous area of the snail takes on the 
appearance of a night sky. Minute luminous 
points glimmer and twinkle like so many 
stars. The luminescence of this animal is in- 
tracellular; no luminous slime goes into the 
surrounding sea water. Among the six species 
of Planaxidae, which were examined, the fol- 
lowing five have the same type of luminous 
organ: Planaxis virgatus , P. longispira , P. peri- 
scelida , P. lineatus , and P. labiosus. P. sulcatus , 
however, has no luminous organ at all. 
EFFECTS OF TEMPERATURE 
No effects are noticable to the naked eye 
in the intensity of luminescence in marine 
snails under thermostimulation. Through the 
use of the highly sensitive 1921 photomulti- 
plier, followed by two stages of amplification 
feeding into a Brown recorder, however, the 
light intensity changes resulting from changes 
in temperature are readily discernible. I had 
the opportunity to make use of such equip- 
ment through the kind offices of Dr. Bernard 
L. Strehler of the Department of Radiobiology 
at the University of Chicago when I visited 
that institution in April, 1954. Our tests were 
extremely interesting. Contained in a small 
glass tube of sea water at a temperature of 
15° C., the snails were placed near the photo- 
multiplier and the temperature of the tube was 
raised and lowered in two successive cycles 
and the light intensity recorded. 
From an initial centigrade reading of 15° C. 
the snails’ temperature was raised to 45° C. 
and lowered to — 10° C. in a period of less 
than 10 minutes. From this point the tem- 
perature was again raised gradually to 60° C. 
and lowered to 15° C. During the first cycle 
the maximum of relative light intensity was 
at 45° C. As the temperature decreased so did 
the intensity, until at — 10° C. it could not be 
detected. 
During the second cycle, however, the in- 
