CONDITIONS OF LIFE 305 



pearl. The affinities of Fierasfer are somewhat doubtful, 

 formerly they were supposed to be related to Ophidiidae and 

 Blenniidae, but from the structure of the skull they seem to be 

 of a more primitive type, and Mr. Boulenger places them in a 

 special division with the deep-sea Halosauridae and a few other 

 forms. 



The sucking fishes of the genera Edieneis and Remora are 

 provided with a curious sucking disc on the dorsal surface of 

 the head by which they attach themselves to sharks, whales, 

 porpoises, turtles and even occasionally to boats or ships. In a 

 broad sense of the word they may be said to be parasites, but 

 they do not feed on their host ; their food consists of other 

 fishes and the advantage of their habit is that it protects them 

 from their enemies and enables them to dart out unexpectedly 

 on prey which they would not be swift enough to pursue by 

 themselves. They may perhaps be regarded as commensals 

 as they probably catch fish which their hosts have pursued for 

 themselves or even devour fragments which escape from their 

 jaws. The sucking disc is a modification of the anterior dorsal 

 fin just as the ventral sucker of the gobies, the lump-sucker, 

 and sucking fish of the family Gobiesocidae, is formed by the 

 pelvic fins. The second dorsal and anal fins are long, placed 

 near the tail, and symmetrical with each other. It is not very 

 difficult to understand how the habit of these fishes and the 

 structural adaptation arose from the habit common to many 

 fishes of lurking under the shelter of any large object in the 

 water, for the purpose of concealment and ambush. The ad- 

 hesive power of the sucker is very great, and on the east coast of 

 Africa the maritime natives make use of the fish for the capture 

 of turtles ; the Remora is attached to a line by a metal ring 

 passed round the base of the tail and taken to sea in a boat ; 

 when a turtle is sighted the fish is put overboard and attaches 

 itself to the animal, which can then be drawn in and captured. 



The Remora was formerly supposed to be one of the Scom- 

 briform or mackerel-like fishes, but is now placed by Mr. 

 Boulenger in a separate division of the Spiny-finned fishes 

 (Acanthopterygians). The celebrated pilot-fish, Naucrates 

 ductor, on the other hand, is placed among the Scombriformes 

 in the family Carangidae, represented by the common scad or 

 horse-mackerel. It is a rather small fish, about a foot in length, 



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