i8 A HISTORY OF FISHES 



sea, and rely on their armour, which here takes the form of a 

 rigid bony case, for protection (Figs. 5B; 42F). Also related to 

 the Porcupine-fishes and Puffers are the gigantic and grotesque 

 Sun-fishes (Molidae), of which there are three species, all widely 

 distributed in warm seas. The Round-tailed Sun-fish (Mola) 

 has a very remarkable shape, the deep, circular and somewhat 

 compressed body appearing as though the tail end had been 

 amputated just behind the high dorsal and anal fins (Fig. 5c), 

 a feature to which the popular name of "Head-fish" refers. 

 Such a body is probably well adapted for a more or less passive 

 drift in ocean currents, and it has been suggested that its 

 curious shape is in some way associated with the peculiar diving 

 habits of this fish. The presence of small deep-sea fishes in the 

 stomachs of captured Sun-fishes demonstrates that they must 

 descend to considerable depths at times. The Round-tailed 

 Sun-fish attains to a length of eight feet or more and a weight 

 estimated at more than a ton. It is a sluggish, and, from all 

 accounts, singularly stupid fish, often to be observed basking 

 or swimming lazily at the surface of the sea. Underlying the 

 skin, which is very tough and leathery, is a layer of hard, 

 gristly material some two or three inches thick — ample 

 compensation for any loss of locomotive power ! 



At the other extreme are the fishes with long bodies, which 

 may be rounded as in the Eels (Apodes) or very much com- 

 pressed, as in the Ribbon-fishes (Trachypteridae) or Cutlass- 

 fishes (Trichiuridae) . From their shape one would hardly 

 expect such fishes to be other than slow swimmers, but, as will 

 be shown below, the adoption of a particular method of loco- 

 motion gives them a greater speed than the short-bodied forms 

 mentioned above. The peculiar shape of the Eel's body (Fig. 

 5f) is almost certainly associated with its habit of living in 

 soft river bottoms, wriggling in and out of the mud, creeping 

 through reeds, or insinuating itself into holes and crevices as 

 do its relatives in the coral reefs. Some of the Eels carry the 

 elongation of the body to such an extreme that they have the 

 appearance of a piece of slender whipcord, and the fins are 

 often much reduced. Such a filiform type of body is charac- 

 teristic of the curious Snipe-eels [Nemichthyidae) , oceanic forms 

 which sometimes descend to considerable depths (Fig. 320). 

 When observed swimming at or near the surface, these Eels 

 are not infrequently mistaken for snakes. It may be noted here 

 that similarity in eel-like form is not necessarily indicative of 

 close relationship, but may be due to that parallelism in 



