CIIIM.^iRA AND ITS CHARACTERISTICS. 



17 



point of their movement they appear in the position shown in fig. 4 p.. A large part 

 of the movement takes place in the dermal web of the fin. Starting from the point 

 marked with an asterisk (*) a wave of movement passes out to the apex of the fin, 

 where its greatest height is shown ; then it passes rapidly around the ventral rim and 

 dies out in the axil. This wave is followed by another, more or less rapidly, accord- 

 ing to the effort of the fish. As the dermal rays are parallel to one another, their 

 fall and rise suggest the movement of the keys of a piano when a finger is drawn 

 across the keyboard. As so much of the conspicuous movement is accomplished 

 by dermal rays, the muscular bases of the fins show to full advantage as balancing 

 organs (cf. fig. 2), almost as in Polypterus. It may be mentioned, in connection with 

 this constant movement, that the dermal margin of the fin is so delicate that it soon 

 becomes ragged by wearing against the sides and bottom of the tank. 



Chima^ra is deliberate in its general movements, suggesting somewhat a shark, 

 but occasionalh' it shows great activity. On one occasion a fish which had been 

 balancing quietlv for some minutes suddenly dashed about the aquarium and 

 then shot up over the side. Ouick movements of the pectoral fins greatly aid the 

 fish's forward propulsion; and in the undulation of the body the dorsals are far 

 more important as swimming organs than the caudal. The ventrals serve rather 

 passively as balancing organs, preserving a horizontal plane and hanging behind 

 like an apron, their median edges overlapping (fig. 4 a). It may be noted that the 

 mixipterygia, which are so conspicuous a feature in museum specimens, are hardly 

 seen in the swimming fish (fig. 41!). They are neatly tucked together behind the 

 ventral fins in the median line and can little impede niovement. In slow forward 

 movement Chimsera rocks somewhat from side to side, the dorsal fin functioning 

 impcrfectlj' as a keel, its spine, by the way, rarely more erect than shown in the 

 figure. In resting the tail droops noticeably* and the fish balances by slow move- 

 ments of the pectorals. The hinder trunk sometimes rests on the prominent pad 

 of the postanal region. (PI. i, fig. 2, c.) 



In further detail: The fish sometimes swims about freely, with a movement 

 described by an observer as "butterfly-like," from the conspicuous flapping of its 

 large pectoral fins. It is more active at night; if placed in a large tank it is apt 

 to swim restlessly from one end of the tank to the other. In daytime it is quieter, 

 and appears to avoid strong light. Occasionally it "sails" or "flutters" to the 

 surface, thrusts its snout out of water, and then, suspending all movements, sinks 

 to the bottom. Here it sometimes rests, balanced on the tips of its fins, like a 

 dipnoan, or Squatina, or even a ray. In this position, when otherwise quiet, its 

 brilliant eyes often show active movements. One receives the impression that 

 captivitv is irksome to the fish, an impression often strengthened by its subsequent 

 behavior, for it will suddenly advance, then retreat, advance again, and sometimes 

 thrust itself out of the water in its attempt to escape. 



*This condition has been recorded in weak, aquarium-bred fishes (e. g., Lepidosteus), but in Chimaera it is 

 probably normal, since it was observed in freshly caught specimens. There is, nevertheless, the possibility of its 

 being due to change of pressure. 



