202 Adaptations of Fishes 



jaw-bones are fused together, and in the Chimasras 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 Avith 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 ineft'ective. 



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 Liparis, are lost alto- 

 gether in Paralipans. The very large poisoned spines of Pterois 

 become very short in Aploactis, the high dorsal spines of Citnla 

 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 

 Scliilbeodcs. 



Relation of Number of Vertebrae to Temperature and the Strug- 

 gle for Existence. — One of the most remarkable modifications 

 of the skeleton of fishes is the progressive increase of the 

 number of vertebrae as the forms become less specialized, and 

 that this particular form of specialization is greatest at the 

 equator.* 



It has been known for some years that in several groups of 



* See a more technical paper on this subject entitled " Relations of Tempera- 

 ture to VertebrEe among Fishes," published in the Proceedings of the United 

 States National Museum for 1S91, pp. 107-120. Still fuller details are given in 

 a paper contained in the Wilder Quarter-Century Book, 1893. The substance 

 IS also included in Chapter VIII of foot-notes to Evolution: D. Appleton 

 & Co. 



