PLAN FOR AN EDUCATIONAL EXHIBIT OF FISHES. 1 325 



The fish in this case illustrate the natural phenomenon of 

 degeneration, or rather specialization to an inactive life. The 



five suborders represented form a graded series of steps leading from 

 fishes adapted to an extremely active existence down to relatively in- 

 active, sluggish forms, incapable of rapid motion, but protected from 

 their enemies by coats-of-mail or by the poisonous alkaloids in their flesh. 



In the left-hand section may be seen the large, active wrasse-fishes 

 and parrot-fishes (Suborder PharYNGOGNATHI) well furnished with 

 means of locomotion (i. e., fins), and with large gill-openings which 

 permit the rapid oxygenation of the blood necessary to swiftly mov- 

 ing animals. The large cycloid scales are evenly distributed over the 

 body and allow the greatest flexibility of movement. The teeth are 

 adapted for seizing, and indicate carnivorous habits. Everything seems 

 adapted to an extremely active life. On the other hand, there is a 

 significant tendency toward fusion in certain bones of the skull, and 

 (e. g., the parrot-fishes) in the teeth as well. This tendency is still more 

 evident in the Scaly-Fin group (Suborder Squamipinnes), where it 

 appears in the fusion of the upper jaw elements, and in the gradual 

 reduction of the gill-slits and the ventral fins. The body becomes later- 

 ally compressed and the transition to the type found in the next suborder 

 (ScLERODERMI) is very clear. This suborder is represented in the 

 upper right-hand section of this case by the trigger-fishes and file-fishes. 

 Here the same flattened form is seen, and the reduction of the spinous 

 dorsal and ventral fins to a few stiff spines is very evident. The bones 

 of the skull have further fused, the gill-opening is a mere slit, and the 

 upper jaw-teeth are compressed or even completely united, while the 

 scales are reduced till, in the file-fishes, they become mere prickles. 

 With the trunk-fishes (Suborder OSTRACODERMI) an immovable box- 

 like armor takes the place of scales; the bones of the skull are almost 

 completely joined; the gill-slit is extremely small; while the ribs and 

 other skeletal elements have been practically reduced to a mere bony 

 axis bracing the weak, soft dorsal, anal, and caudal fins. The spinous 

 dorsal and the ventral fins have disappeared. 



Finally, in the puffers (Suborder GymnodonteS) we have the last 

 stage of degeneration or specialization to a sluggish existence. Scales, 

 spinous dorsal fin, and distinct teeth are gone. Pelvis, ribs, and caudal 

 vertebrae are degenerate and, in extreme forms, even absent. The 

 remaining fins, like those of the trunk-fish, are weak, and the body 

 incapable of rapid motion, while the leathery skin, power of inflation, 

 and poisonous flesh act as protective factors. The largest example of 

 the group, the head-fish or mola, sluggishly floats on the surface of the 

 sea, leading an inactive and lazy existence. 



Fig. 5. — An accessory label to illustrate a biolo^cal phenomenon. 



