EVOLUTION— PYCRAFT 237 



fin. In the second there are two conspicuous rays to the dorsal fin, 

 and the pelvic fin has taken the form of two rodlike rays of unequal 

 length. The pectoral has greatly increased. The third stage shows 

 four dorsal fin rays, two subequal and greatly enlarged oarlike ven- 

 tral rays, and still a tapering tail. Further, it should be noted that 

 a fin membrane, unsupported by rays, runs continuously along the 

 body from the dorsal fin backward and forward to the vent, as in 

 the earlier stages. In the fourth stage the dorsal fin rays number 

 five, but much increased in size and changed in shape. The pelvic 

 fin rays have materially changed in shape and proportions, the lower- 

 most extending backward as a long filament far beyond the body. 

 The tail no longer tapers backward. Its extremity has turned upward. 

 Herein is indubitably an ancestral character, recalling the tail of the 

 shark tribe, which have a more ancient ancestry. Above the upturned 

 portion is a relic of the earlier continuous fin membrane, and below 

 it are a series of fin rays that will remain to form an apparently 

 "hormocercal" tail after the upturned portion has been absorbed. 

 This transformation from the upturned, or "heterocercal" sharklike 

 tail fin is found in nearly all the higher fishes during larval life. 

 It is a "recapitulation" of an ancestral character. It repeats this 

 stage because it is still following the "route" along which the hormo- 

 cercal tail traveled in the course of its evolution. There are some 

 cases where a short cut has been taken by missing out the upturned 

 phase. Finally, note that out of that continuous fin membrane two 

 new fins have appeared, a second dorsal and an anal fin, and there 

 are still traces of the earlier, rayless fin, at the base of each. 



Now compare these with the strikingly different adult stage, which 

 is characterized by its enormous head and mouth, strangely de- 

 pressed, so that the head is no longer round, but flat. The eyes 

 are no longer on each side of the head, but look upward, side by 

 side. The pectoral fins now project at right angles from the body, 

 and lie flat, with the head, on the sea floor. The body has, in short, 

 been transformed from that of a free-swimming fish to a sedentary. 

 Instead of hunting for food in midwater as in its infantile stage, 

 it now lies flat on the bed of the sea. And other and very remark- 

 able changes have followed this changed mode of life. Briefly, the 

 rays of the dorsal fin have become widely spaced. The first dorsal 

 has shifted forward to the snout and developed at its free end a 

 flaglike fold of skin. At the same time the enormously enlarged 

 mouth and the sides of the head have developed similar "tags of 

 skin" forming a fringe. These can be set in vibration and look 

 like pieces of seaweed, moved by the currents. The "flag" on the 

 snout is used as a lure, being gently waved when small fish are in 

 the neighborhood. Presently they draw near to investigate, when 



