Bliss.] 



12 [June 15, 



crest and fits closely under the shoulder of the large spine in front 

 of it. The third spine is also raised by the tendon connecting it 

 with the second. When erect, any pressure upon the large spine 

 forces its shoulder against the protuberance on the second, which 

 is supported by its crest and by the extremities of its arms, so that 

 a backward movement of either of the spines is impossible, and the 

 large spine is rendered serviceable as a weapon. If now the third 

 spine be pushed down, the tendon which connects it with the second 

 causes this latter to rise and ride over its crest, which thus allows 

 the first spine to be readily depressed by appropriate muscles 

 attached to its base. 



The operation of this peculiar apparatus much resembles that of a 

 lock of a gun, and has given to the fish its common name of " trig- 

 ger "or " cock fish." 



Thus it is seen that the principle of the working of this apparatus 

 is the same as in Boras, though the means by which it is accom- 

 plished are somewhat different. In Doras it is the third spine which 

 is enlarged to serve as a weapon ; while in Balistes it is the first. In 

 Doras the large spine maintains its erect position by pulling the 

 small spine in front of it' against its crest. In Doras only two spines 

 compose this weapon, the first of which must be moved before the 

 second can be ; in Balistes three spines enter into the structure of 

 the apparatus ; the third to be moved before the position of the other 

 two can be altered. Equal support is obtained in both ; but in the 

 one case resistance results from a pulling movement from behind ; 

 and in the other from a pushing movement from before. 1 



i For further information regarding the fin structure >of Balistes and allied fam- 

 ilies see Hollard's Monograph of the Balistidce in Annales des Sciences Xaturelles, 

 Vol. xx, 3me Ser., p. 101, 1853 ; Meckel's description of Balistes in his System der 

 Vergleichenden Anatomie, Theil u, pp. 239-242, 1824; Bruhl's '* Osteologisches aus 

 dem Pariser Pflanzengarten, p. 58, et seq. and L. Agassiz' Poissons Fossiles, Tom. 

 n, Pt.2, p.249. 



