74 Adaptations of Fishes 
jaw-bones are fused together, and in the Chimeras they are 
solidly joined to the cranium itself. 
The Angler-fishes.—In the large group of angler-fishes the first 
spine of the dorsal fin is modified into a sort of bait to attract 
smaller fishes into the capacious mouth below. This structure 
is typical in the fishing-frog (Lophius), where the fleshy tip of 
this spine hangs over the great mouth, the huge fish lying on 
the bottom apparently inanimate as a stone. In other related 
fishes this spine has different forms, being often reduced to a 
vestige, of little value as a lure, but retained in accordance 
with the law of heredity. In a deep-sea angler the bait is 
enlarged, provided with fleshy streamers and a luminous body 
which serves to attract small fishes in the depths. 
The forms and uses of this spine in this group constitute a 
very suggestive chapter in the study of specialization and ulti- 
mate degradation, when the special function is not needed or 
becomes ineffective. 
Similar phases of excessive development and final degrada- 
tion may be found in almost every group in which abnormal 
stress has been laid on a particular organ. Thus the ventral 
fins, made into a large sucking-disk in Lrparis, are lost alto- 
gether in Paraliparis. The very large poisoned spines of Pterois 
become very short in Aploactis, the high dorsal spines of Cztula 
are lost in Alectis, and sometimes a very large organ dwindles 
to a very small one within the limits of the same genus. An 
example of this is seen in the poisoned pectoral spines of 
Schalbeodes. 
The Unsymmetrical Eyes of Flounders.—In the two great 
families of flounders and soles the head is unsymmetrically 
formed, the cranium being twisted and both eyes placed on the 
same side. The body is strongly compressed, and the side pos- 
sessing the eyes is uppermost in all the actions of the fish. 
This upper side, whether right or left, is colored, while the eye- 
less side is white or very nearly so. 
It is well known that in the very young flounder the body 
rests upright in the water. After a little there is a tendency to 
turn to one side and the lower eye begins its migration to the 
other side, the interorbital bones or part of them moving before 
