Observations on the Pyrocystece. 183 
dcrablc body of evidence. It is quite out of analogy with other 
luminous organisms, and would be a matter of considerable 
difficulty to prove in this species, where the nucleus is imbedded in 
a mass of protoplasm. When the organism is crushed between 
the fingers the crushed substance continues luminous for a few 
seconds (as is the case with the Noctiluca ); and also when exposed 
and drying it in the air, it gives out light and remains luminous for 
a short time. 
Alcohol and other chemical substances are usually described as 
direct agents in the production of the luminosity of organisms 
such as Noctiluca , but in Pyrocystis, at least, it would seem that 
alcohol does not act so much directly—for on merely mixing it 
with the water containing the organisms, very little effect is 
produced—but, by raising the irritability of the protoplasm, causes 
it to re act more violently to the shaking stimulus. The mechanism 
of light production in this and other luminous organisms is, of 
course, quite obscure. It is, however, interesting to note that a 
considerable number of chemical bodies, which are to be found 
in living organisms, such as lecithin, cholesterin, ethereal oils, 
grape-sugar, etc,, under certain circumstances become luminous, 
and that their luminosity is increased by shaking. The light pro¬ 
duced in these cases depends on slow oxidation, and it is therefore 
possible to imagine that the luminosity of Pyrocystis and other 
organisms depends on the presence in the cell of these and similar 
substances; the effect of shaking, etc., being to bring about more 
rapid oxidation, either by the increased supply of oxygen, or perhaps 
by some direct effect on the irritability of the living protoplasm. On 
the death of the cell-substance, all luminosity seems to disappear. 
(For an interesting discussion on the luminosity of Noctiluca, see 
Biitschli (1). 
P. Fusiformis, Wyv. Thoms. 
This species, as it name implies, is spindle-shaped in form, and 
attains to a length of 1mm. Fig. 9 shows it in the resting and 
and slightly contracted state, while in the “Challenger” narrative 
two figures are given of what is apparently a stage in the process 
of division. The nucleus is more or less spherical in shape (fig. 10), 
but apart from this and the external form, the general arrangement 
of the cell is similar to that of the first described species. There is 
the same collection of protoplasm at one point of the cell, in this 
case the middle of the long axis, from which cytoplasmic strands 
radiate out to the rest of the cell. A large number of oil globules 
