CONDITIONS OF LIFE 307 



Islands off the west coast of Ireland. The log was covered 

 with barnacles on which the fish, of which there were several 

 hundreds, were feeding. The islanders were so frightened at 

 the strange fish, which they declared were sheogues or fairies, 

 that they all ran away, and an old man who took some home for 

 eating was not allowed to take them into his house. Another 

 species, Lirus medusophagns, has received its specific name, 

 meaning " feeding on jelly-fish," from the fact that at least 

 when young it is constantly found sheltering, like the young of 

 our own Gadidae, under large medusae in the open ocean, but it 

 is not known to feed on such animals. Another species of the 

 family, Nomeus gronovii, distinguished by its very large pelvic 

 fins, has been observed in New South Wales to live habitually 

 beneath the Portuguese man-of-war, Physalia, as many as ten 

 specimens of the fish being found under one of the Physalia, 

 and when the latter are driven ashore the fish are often stranded 

 with them. It has been suggested in this case that the fish is 

 unaffected by the poison of the tentacles of the Physalia and 

 that it feeds on the animals killed by the jelly-fish. Nomeus is 

 only about three inches long. 



Parasitism is rare in fishes. The curious habit of the little 

 Siluroid Vandellia cirrosa. can scarcely be called parasitism, as 

 it is only accidentally and occasionally exercised. This fish is 

 only 6 cms. or 2i in. in length, and only about an eighth of 

 an inch in diameter ; it is believed by the natives of the banks 

 of the Amazon to enter the urethra of men bathing, being at- 

 tracted by the urine, and it is said that when it has once 

 entered it cannot be pulled out again because of the spines on 

 its opercula. Whether the belief is well founded or not, it is 

 certain that the natives protect themselves from the fish by 

 wearing, when bathing, a special shield formed of a small 

 perforated cocoanut shell. 



True parasitism is exhibited by another small Siluroid, 

 namely, Stegophilus insidiosus, which lives in the gill-cavity of 

 large species of the same family, especially Platystoma coruscans 

 which grows to a length of six feet ; the parasite and its host 

 are also South American fresh- water fishes. In this case the 

 parasite sucks blood from the gills of its host. 



External differences between male and female are less con- 

 spicuous in fishes than in mammals and birds, but are neverthe- 



