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Luminosity of Marine Animals. [December; 
VIII. THE CAUSE AND THE PURPOSE OF THE 
LUMINOSITY OF MARINE ANIMALS. 
< 2^1 
S N the opening address delivered by Prof. H. C. McIntosh 
before the Biological Section of the British Association 
the phosphorescence of marine animals was discussed 
at some length. The author gave an enumeration of the 
various groups of animals possessing this power, and 
described the manifold phenomena manifested. In conclu- 
sion he took into consideration the cause and the purpose 
of this phenomenon. 
As he remarked, in the Protozoa the structure of the 
minute, and often very numerous, creatures which evince 
phosphorescence shows plainly that the presence of a defi- 
nite nervous system is not necessary for its manifestation. 
The protoplasm of their body is itself sufficient for its pro- 
duction. Here there are no glands for the secretion of 
luminous substances, and in many there is evidently no fat 
which might undergo slow combustion. In the Ccelenterata 
the phenomenon seems to stand in close relation to nervous 
processes, though in certain cases the luminous substance 
possesses quite peculiar properties. Whilst in certain 
Annelida, such as Chatopterus and Polyerrus, there exist 
glands which may effeCt the secretion of a luminous sub- 
stance in certain Polynoides, the emission of light seems 
to be due to a peculiarity of the nervous system. The irri- 
tability in the phosphorescent species of the latter family 
fluctuates greatly, some — e.g., Polynoe scolopendrina — being 
sluggish, and others, on the contrary,— like Harmothoc , — 
exceedingly sensitive. In the Crustacea the luminous pro- 
perty seems to possess the character of a secretion, which 
is probably under the control of the nervous system. In 
Pyrosoma and Pholas dactylus a luminous secretion is a pro- 
minent attribute ; and in the latter, as in the Annelida, 
death occasions its manifestation, which, to a limited extent, 
holds good in fishes also. 
It is hence plain that the cause of phosphorescence is 
complex. In one group of animals it is derived from the 
formation of a substance which can remain behind like a 
luminous trail. The ease with which, in Pennatula and 
and other Ccelenterata, phosphorescence can be repeatedly 
