| Abstract: | Résumé 1. 1. There is a symbiosis between Sertularia operculata and Squalus acanthias, and between Seralia lendigera and Hippocampus ramulosus—there being but a single case reported for each pair of organisms. It is probable that these associations are entirely accidental. 2. 2. Of Stylactis minoi and Minous inermis, no fewer than twenty-nine specimens of the fish (presumably all ever taken) wherever found—and they have been taken from five widely distant stations on both coasts of India, and from Japan—were infested with the hydroid. Furthermore, so far as known, this particular hydroid has never been found save on this particular fish (inermis). These facts would seem to indicate that this is a purposive or obligate symbiosis. 3. 3. About one hundred specimens of Hypsagonus quadricornis were taken in Puget Sound. Thirty-seven of these were preserved, and ten of them were found to be sparsely covered with Perigonimus pugetensis. Other specimens of the fish taken outside Puget Sound and in Behring Sea all lacked the hydroid. Consideration of all these facts leads to the conclusion that the association is symbiotic and more or less accidental. 4. 4. One case has been presented of Hydrichthys mirus attached to Seriola zonata in Narragansett Bay. Parasitism is alleged, but the proofs offered, that there was some apparent degeneration on the part of the hydroid and some slight evidence of wasting away of the muscles of the fish at the point of attachment, are at best inconclusive, there being no evidence from sections presented to show actual anastomosis of the tissues of the two organisms. From the evidence presented one must conclude that this is only a case of symbiosis. 5. 5. One case is known of the attachment of a Nudiclava to a fish, Monacanthus, from the Andaman Sea. Parasitism is alleged in the title of the paper, but disclaimed in the text, since, in sections cut through the basal plate and the skin to which it was attached, such was not proven. Furthermore, the finding of food in the hydranths discounts the idea of parasitism. This case also must be classed as a symbiosis. 6. 6. True parasitism has been repeatedly shown to exist between an aberrant hydroid, Polypodium hydriforme, and the ovarian eggs of the Volga sterlet, Acipenser ruthenus. This has been definitely established by the work of four investigators, extending in time from 1872 to 1922—a half century. Except in its earliest stages, Polypodium has the nutritive cell-layer of its stolon, the endoderm, on the outside bathed in the egg-yolk. Later this becomes inverted and a large amount of yolk is carried into the common cavity. The egg is used up in nourishing the parasite. 7. 7. True parasitism has been shown between Hydrichthys boycei and numerous individuals of three species of fishes—Ambassis natalensis, Mugil sp., and an undetermined fish belonging to the Glyphidodontidæ—in Durban Bay, South Africa. The parasites were attached to various parts of the fishes, especially the fins. At the points of attachment, haustoria were sent down into flesh and into blood-vessels, and by means of these the parasite fed on the tissues of its host. Furthermore, on none of the hydranths were tentacles ever found, nor was any food ever found in them. Strange to say, the parasite never covers any large area of the fish, and apparently presently drops off leaving a scar behind. |
