1 62 FISHES CHAP. 



the Fish to hop about the muddy or sandy flats left bare by the 

 retreating tide, in]Dursuit of the small Crustaceans on which it 

 feeds. In other Teleosts certain of the rays of the pectoral fin 

 separate from the rest and from one another, and form free 

 tentacle-like structures the use of which is probably tactile. In 

 the Gurnards these organs are relatively short and stout, but in 

 other Fishes they may form long slender filaments twice as long 

 as the animal, and capable of being moved independently of the 

 fin, as in the West African and West Indian species of Poly- 

 nemidae {Pentanemus quinquarius). Similar free rays are also 

 present in some deep-sea Scopelidae, as in Bathypterois dubms, 

 where they are nearly as long as the Fish itself (Fig. 371, B). A 

 familiar modification of the pelvic fins in several Teleosts is their 

 coalescence and more or less complete conversion into a ventrally- 

 placed sucker- like organ of attachment, as in the common Lump- 

 Sucker iCydofUrus) and the Gobies (Gobius). In the gaudy 

 Chilian Fish, Sicyases sanguineus (Fig. 428), the anterior part 

 of a huge ventral sucker is supported by the jugular pelvic 

 fins, and the hinder part by prolongations from the pectoral 

 girdle. Certain Cyprinidae (e.g. Gastromyzon, which frequents 

 the rapidly-flowing mountain streams of Borneo), have the whole 

 ventral surface of the trunk, in conjunction with the outwardly 

 and horizontally directed pectoral and pelvic fins, modified to 

 form an efficient adhesive surface for attaching the Fish to 

 the stones and rocks of the river bottom^ (^ig- 355). In the 

 males of Elasmobranchs, except in the Palaeozoic Shark Clado- 

 selache, and of Holocephali, the hinder portions of the pelvic fins 

 are modified to form copulatory organs, the claspers, mixipterygia, 

 or pterygopodia. Lastly, it may be mentioned that the spines, 

 often long, pointed, and sometimes serrated, with which the paired 

 and median fins of many Fishes are provided, furnish formidable 

 offensive or defensive organs, especially when they are associated 

 with poison glands, and also that in by no means an inconsider- 

 able number of Teleosts the spines may form part of a stridulating 

 vocal mechanism. 



In different Fishes the pectoral and pelvic fins and the 



' Sucker-like modifications of the ventral surface of tlie body, in which the 

 paired fins take no part, are present on the throat in many Fishes which frequent 

 hill-streams, as in some small African and Asiatic Cyprinidae (e.g. Discognathus) 

 and a few Siluridae (e.g. Sui/lyptosternum). 



