Mr Potts, The Swarming of Odontosyllis. 197 
| 
| aspects the swarming in this species resembles that in 0. phosphorea, 
we. in the appearance of great numbers of individuals at the surface 
of the sea at definite times of the year and at a definite period of 
the day in the neighbourhood of sunset. But the divergencies in 
the habits of the two species are very interesting. While O. phos- 
phorea first reaches the surface well before sunset, O. enopla is not 
seen till dusk has fallen. In this latter species, moreover, the 
phosphorescence, which is characteristic of most species of this 
genus, is developed to a most extraordinary extent and is adapted 
to serve as a means of sexual recognition. This is almost without 
parallel in the animal kingdom. It is, however, stated that the 
function of the phosphorescent organs in the Fireflies is to attract 
the other sex. In the case of the common glow-worm it is generally 
allowed that the male finds the female by means of her phos- 
phorescence. Mr J. C. F. Fryer has told me of a Lampyrid beetle 
in Ceylon, the female of which actually remains in deep holes, but 
that she emits a most powerful light from organs on the underside 
| of the abdomen, which is the better displayed by the flexion of that 
part of the body. As soon as the male approaches, however, the 
light dies down as in Odontosyllis. The account of O. enopla, 
which I have quoted above at length, shows, however, that we 
have among much lower animals almost as complex a phenomenon 
in which the production of phosphorescence is equally essential for 
the meeting of the sexes. It is possible, however, to make one 
criticism of the interpretation which is given above. This is that 
an arrangement to secure close approximation between the male 
and female of a marine worm would seem in general to be un- 
necessary for the successful propagation of the species. There is 
none such in O. phosphorea, and in the case of our two commonest 
‘British species of Odontosyllis, O. ctenostoma and gibba, the hetero- 
‘syllids seem to occur, not in swarms, but as scattered individuals, 
and probably discharge their eggs or spermatozoa when no other 
‘member of the species is near. In the only reference respecting 
the pelagic occurrence of these species that I am able to find 
Gravely* says: “The brown Odontosyllis (i.e. O. gibba) is frequently 
‘seen in the adult condition—occasionally accompanied by 0. cteno- 
stoma and sexual specimens of Autolytus and Myrianida—swimming 
at the surface of the sea at the mouth of Port Erin Bay and further 
out towards the Calf on calm evenings during July.” This passage, 
I think, clearly points to an irregular and sporadic occurrence. 
me if there are these considerable differences in the reproductive 
habits of the different species there must, I think, be equivalent 
physiological differences in the reproductive cells of the species. 
‘One would expect, from the elaborate devices practised by O. enopla 
to ensure fertilisation, that the independent life of the eggs and 
* Q. J. M.S8., vol. ti. p. 600. 
