506 G. H. PARKER 
rate is essentially identical with that obtained from the same 
bands for the waves of phosphorescence (7.39 em. per second), 
and suggests that these two activities, phosphorescence and the 
withdrawal of autozodids, are controlled by the same kind of 
transmission. 
Having found that the rate of transmission of the impulse 
to zodid withdrawal at a temperature of 21°C. was the same as 
that for the wave of phosphorescence at the same temperature, 
an attempt was made to ascertain whether change of temperature 
influenced the rate of withdrawal as it did that for phosphor- 
escence. But the withdrawal of zodids is a much less accurately 
timed operation than the passage of a wave of phosphor- 
escence, and I found it impossible to obtain accurate time read- 
ings for withdrawal. At 11°C. the rate at which the withdrawal 
wave traveled was certainly much slower than at 21°C., but how 
much slower could not be determined with accuracy In a few 
instances where the attempted determinations seemed especially 
clear and decisive the times ranged from 2.6 seconds to 3 seconds 
for a stretch of 9.24 em. Assuming the average time to be 2.8 
seconds, this yields a rate of 3.3 em. per second, which is very 
close to that found for phosphorescent transmission at this tem- 
perature, namely, 4 cm. per second. But these determinations © 
were too few in number and too scattering to be relied upon, and 
the only conclusion that I feel justified in drawing from them is 
that the rate at 11°C. is slower than at 21°C. 
If actual determinations were difficult at 11°C., they were 
quite impossible at 31°C. At this temperature the wave often 
seemed much quicker than at 21°C., but its beginning and end- 
ing were each so-vague and indistinct that it was impossible, 
even by watching individual terminal zoéids, to obtain any reli- 
able readings. The most that can be said for this aspect of the 
question is that with increased temperature the wave for with- 
drawal appears to increase its rate. 
When these two forms of transmission, that for phosphores- 
cence and that for zodid withdrawal, are compared, they are found, 
as must have been evident from the foregoing account, to be 
strikingly similar. They both spread through the colony in the 
