1052 REPORT—=1885. 
the presence of a well-defined nervous system is not required for its manifestation, 
the protoplasm of their bodies alone sufficing for its development. There are 
no glands for secreting it, and in some apparently no fatty matter for slow 
combustion. In the Ccelenterates the phenomena appear to be more nearly 
related to nervous manifestations, though in certain cases the luminous matter 
possesses inherent properties of its own. While in some annelids, such as 
Chetopterus and Polywrrus, there are glands which may be charged with the 
secretion of a luminous substance, it is otherwise with certain Polynoide, in which 
the emission of light appears to be an inherent property of the nervous system. 
The irritability in the phosphorescent examples of the latter family, however, 
varies considerably, some, e.g., Polynoé scolopendrina, being sluggish, while others, 
like Harmothoé, are extremely irritable. In the Crustaceans the luminosity seems 
to have the nature of a secretion, probably under the control of the nervous system. 
In Pyrosoma and Pholas dactylus a luminous secretion is also a prominent feature, 
and in both the latter and the annelids decay excites its appearance, as also is the 
case, to a limited extent, in fishes. 
It is evident, therefore, that the causation of phosphorescence is complex. In 
the one group of animals it is due to the production of a substance which can be 
left behind as a luminous trail. The ease, for instance, with which in Pennatula 
and other Ccelenterates the phosphorescence can be repeatedly produced by friction 
on a surface haying a minute trace of the material, clearly points to other causes 
than nervous agency. On the other hand again, as in certain annelids, it is purely 
a nervous action, probably resembling that which gives rise to heat. The action, 
moreover, evidently affects the organic chemical affinities of the tissues engaged. 
With the exception of such as Macartney, the older authors, who in some 
cases took an imaginative view of the question, connected the emission of light 
with the special economy of the deep sea. The speculations to this effect are 
fairly summarised in ‘ Brewster's Edinburgh Encyclopedia,’ published in 1830," 
Thus it is supposed that total darkness exists at the depth of 1,000 feet, and that 
the phosphorescence of marine animals is a substitute for the light of the sun, 
Moreover, that by these lights the animals on the one hand are guided for attack, 
and on the other their power of extinguishing them enables them to escape 
destruction. Fishes are known to prey chiefly at night, and the writer supposes 
that the phosphorescence of their prey guides them; for, he says, this luminosity 
is particularly brilliant in those inferior animals which from their astonishing 
powers of reproduction, and from a state cf feeling little superior to that of 
vegetables, appear to have been in a great measure created for the food of the 
more perfect kinds. Dr, Coldstream at a later period (1847) reproduced the same 
views in his article on animal luminosity.* 
The same notion was brought forward in the ‘ Report of the Cruise of the 
“Porcupine.” ’* and special reference was made to the young of certain starfishes, 
which are stated to be more luminous than the adults, that being part of the general 
plan which provides an excess of the young of many species, apparently as a 
supply of food, their wholesale destruction being necessary for the due restriction 
of the multiplication of the species, while the parent individuals, on the other 
hand, are provided with special appliances for escape or defence. Thus phosphor- 
escence, it is further asserted,* in very young Ophiacanthe just rid of their plutei, 
in a sea swarming with predaceous crustaceans, such as Dorynchus and Munida, 
with great bright eyes, must be a fatal gift. Some naturalists still appear to 
hold a similar, though perhaps modified, view. Much caution, however, is neces- 
sary in theorising on this head. 
In the first place, phosphorescent animals do not appear to be more abundant 
in the depths of the sea than between tide-marks or on the surface, the latter 
perhaps presenting the maximum development of those exhibiting this phenomenon. 
! Chiefly the views of Dr. Macculloch. 
? Todd’s Cyclop. of Anat. and Phys. 
3 Proc. Roy. Soc, No. 121, 1870, p. 432. 
* Depths of the Sea, p. 149. 
