COXIPAHATIYE STUDY OP SCOMBROID FISHES. 355 



«lirticnlt to iiudorstiui»! that Acanihocyhiuin wliicli is always found ncnx tlie 

 surface 1ms & well develojxHl fiir-blaiWer, wliile Cijhium niphonium whic^li has 

 a rather xvide range of vertical (ILstril.mtion lacks it. The aii'-bhulder is more 

 or less fusiform, aud fjonerally thickened at the anterior pvii. 



In the Scombridae the air-l)Iadder is generally present, l)eing absent in 

 Scomber scombrus only. In Scomber japonicus the air-bladder is fusiform, 

 naiTow and pointed at both ends. It occupies a httle more tlian half the 

 length of the abdominal cavity. Its wall is very thin. 



In the CybiicLie the air-bladder is not foimd in Cyhmm niplwnium, G- 

 koitanum, and Scmla oricnkdia. In Gyranoaanla nuda the air-bladder is 

 lai^ and thick- walled. 



Fig. L. .\ir-blndder of tnanies. 1, Thunmts germo (dorsal and side views); 

 2, Tkunnus orietitalls dorsal and side views); 3, Parathtmnus mebachi (dorsal 

 and side views) ; 4, Xeothimnus macropterus (ventral viewj. 



In the Thimuidae the development of the aii" -bladder is very interesting. 

 In Thunnns (jermo the air-bladder is naiTow, but long, nmning the whole 

 length of the abdominal cavity, and has a median dorsal swelhng at the 

 jinterior end. In T/amnns orientcdis the air-bladder is triangular, veiy wide, and 

 sti'aight at the anterior end, occupying the entire breadth of the abdominal cavity, 

 but it is short, and becomes gradually narrow Ijehind, pointed at the posterior 

 end. It is a httle longer tlian half the length of the alxlomiual cavity. The 

 external wall is imifoiioly thin. The internal wall is finely reticulated. At 

 the middle of the roof of the air-bladder, there is a large roimd hole, which 

 leads to an accessory conical ca\aty, extending from the hole behind to the 



