Notes on Myriapoda, 15 
lowered and the animal is secured with the two electrodes in 
contact with its body. The current can then be applied by 
laying contact wires from the induction-coil one upon each 
electrode of the holder and completing the circuit in a dark- 
room by means of a switch or push. A slight modification 
of this arrangement makes it possible to observe controlled 
luminosity under the microscope (PI. I. fig. 8). 
For photographic records of luminosity we have adopted a 
different method. In this case, in order to obviate the 
possibility of a photographic record of stray electric sparks, 
it is safest to use pressure alone to stimulate light-produc- 
tion. It is necessary to carry out the experiment in a 
photographic dark-room. ‘lhe lower glass plate of the 
ordinary holder is replaced by a piece of photographic film 
with the sensitized surface placed downwards (outwards), so 
that no contact action,upon the prepared surface of the film 
cau be initiated by the secretions of the centipede’s body. 
The upper glass plate of the holder is replaced by a dull 
metal sheet. The animal is then allowed to crawl upon the 
back of the photographic film and upon it is laid the metal 
plate. Pressure upon the metal sheet stimulates luminosity, 
which is photographically recorded on the film (PI. II. 
fig. 13). The animal should be killed immediately by 
dropping it into methylated spirit. 
In taking microphotographs of the ventral surface of 
these centipedes to show such features as the pore-field 
and the integumentary glands the holder is again employed 
upon the stage of the microscope, but it is well to weigh 
evenly the uppermost plate as an additional precaution 
agaiust slight body-movements. Insuch cases the movement 
of walking appendages may be neglected (PI. I. fig. 9). 
In the estimation of the intensity of light we have not 
attempted any very delicate measurement. In some early 
experiments we were entirely guided by the eye, and taking 
the initial intensity as our standard we gave it the arbitrary 
designation 10. Later we found that a luminous powder 
used by clockmakers when mounted in Canada balsam served 
a useful purpose ; we estimated the initial luminosity of a 
stimulated centipede to be about 100 times brighter, and with 
this assumption, taking the luminosity of the test-slide of 
clockmaker’s powder as one unit of brightness, we were able 
the apparatus is often easier to manipulate when the electrodes are free, 
and this because ditliculty is: generally experienced in keeping the 
animal in its proper position until it is secured by gently lowering the 
upper plate upon it. 
