In the 'Report of the British Association' for 1887 (p. 767) we have a note by Mr. Harker "On a Luminous Oligochæte." But here again the same remark applies. Much good work, alas! is rendered valueless for want of a little accuracy in nomenclature.
It now becomes a question what end could be served by the possession of this property. The philosopher no sooner learns a new fact than he begins to pry into the secret which lies beneath, and stands to it as cause to effect. We have analogy to guide us. The water worms may be compared with the marine animals which produce phosphorescence, while the Brandling may be studied in the light of a Glowworm. It may be objected that as worms, except in a few rare cases, have no eyes there can be no advantage in their luminosity. But such an argument would be based on the erroneous assumption that a creature without eyes is incapable of receiving impressions from light. That worms are influenced by light is proved both by their habit of avoiding it, and by the experiments which have been carried out by various students. Darwin remarks that as worms are destitute of eyes he at first thought that they were quite insensible to light. He found, however, that "light affects worms by its intensity and by its duration." Hoffmeister states that, with the exception of a few individuals, worms are extremely sensitive to light, and from my own observations I have been able to demonstrate that there are marked differences in the susceptibility of the different species—some being very much more susceptible than others.
Now it follows that if a number of species of worms lived together in one place, as they usually do in a manure-heap, it would be a great advantage for a given species to possess a distinguishing feature, such as that of luminosity, to enable two individuals to discover each other's whereabouts, just as the male Glowworm detects the female by the light emitted from her upturned abdomen.
Viewed in this light, a new field of research is opened up which hitherto has been totally unworked, but which may be hoped to yield remarkable results if diligently, patiently, and intelligently tilled.
It will not be out of place in this connection to quote from
