"In most of the fishes examined by him, the author found the stomach empty; it was full only in one. The contents of the stomach had the appearance of a lump of fat, and consisted of half-digested muscle. Under the microscope, striated muscular fibres could be detected, and the author thinks that they belonged to the muscles of a fish. This circumstance proves that Oxybeles does not feed upon the chyle of the star-fish, but that its nourishment is analogous to that of other fishes. Whether it seizes upon the fishes taken by the star-fish for its own nourishment must be determined by further investigations.
"The author's observations establish—
"1. That Oxybeles gracilis is not a true parasite.
"2. That it passes the greater part of its life in the stomach of Culcita discoidea, as is also indicated by the unusually pale colour of the fish.
"3. That, however, it can come out, either to seek nourishment, or for the purpose of reproduction.
"4. That it returns to the mouth along the furrow on the ventral surface of the arms.
"5. That it is very sensitive to light.
"6. That it feeds upon other animals.
"In fresh water the animals live for about half-an-hour. The pigment upon the peritoneum exhibits under the microscope the most beautiful stellate forms. The fish possesses a swimming-bladder."[232]
Some very curious instances of parasitism occur, in which one kind of creature compels or induces another creature to labour for its special benefit. Indeed, in all cases, the parasite is benefited by the functions of the supporter; but, in the cases I refer to, the slavery is more special and more apparent.