162 FISHES CHAP. 
the Fish to hop about the muddy or sandy flats left bare by the 
retreating tide, in pursuit 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 thte animal, and capable of being moved independently of the 
fin, as in the West African and West Indian species of Poly- 
nemidae (Pentanemus quinqguarius). Similar free rays are also 
present in some deep-sea Scopelidae, as in Bathypterois dubius, 
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 (Cyclopterus) 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’ (Fig. 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 the 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. Huglyptosternum). 
