PILOT-FISH. ]G9 



The Pilot-fish, Numerates ductor, 725, and fig. 79, is a pelagic Pilot-fish, 

 fish found in association with large fish, especially Sharks. It is 

 named Pilot-fish because of its supposed habit of conducting 

 the Shark towards suitable prey. The association with the Shark 

 may, however, be possibly due to the fact that the Naucrates 

 feeds on the parasites that infest the Shark, and also on small 

 pieces of flesh that escape the Shark when feeding, while the 

 well-established fact that the Pilot-fish is not attacked by the 

 Shark may rather find its explanation in the superior agility 

 of the former than in any sentimental reciprocity on the part 

 of the Shark. The Pilot-fish is known to follow ships for long 

 distances for the sake of the refuse thrown overboard, but it 

 usually deserts the ship on nearing land. It occurs in all 

 tropical and temperate seas and attains a length of about twelve 

 inches. The remaining Carangid fishes exhibited are of no special 

 interest. 



At the top of Wall-case 17 the family Trichiuridae is represented Wall- 

 by the Hair-tail, Trichiurus lepturus, 739, and the Scabbard-fish, case i7 * 

 Lepidopus caudatus, 738, Ruvettus pretiosus, 741, and Thyrsites 

 atun, 740. In the Trichiuridae the premaxillary bones are not 

 protractile as they are in the previous family, the Carangidae ; 

 the body is elongate and laterally compressed ; the spinous 

 portion of the dorsal fin is much longer than the soft portion 

 and the spines more or less feeble; there are no free spines to the 

 dorsal and anal fins ; the pectoral fins are set low down the sides 

 of the body, the scales are small or absent. The fishes of this 

 family are pelagic and widely distributed, and many occur at 

 great depths. In the Hair-tail (739) the body is ribbon-like, Hair-tail. 

 and tapers to a point behind, there being no caudal fin ; in the 

 Scabbard-fish (738) the dorsal fin is not divided into spinous 

 and soft portions, and the pelvic fins are wanting. Two other 

 fishes belonging to this family, Lepidopus tenuis, 971, and 

 Aphanopus carbo, 982, are shown in the case of Deep-sea 

 Fishes, Cabinet-case 44, and a specimen of EuoxymetojJon poeyi, 

 1096, six and a half feet long, from Mauritius, is shown elsewhere 

 in the Gallery. 



