34 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



progression in the water. Those attached to the pectoral are often 

 nearly as long as the &a itself. A series of large shield-like scales 

 cover the bases of these fins, apparently with the same object as the 

 axillary scales. These are particularly large in the species from the 

 Gulf of Mexico. 



Scales. 



50. The scales are, in the young fish, arranged in comparatively regu- 

 lar rows. In adult specimens of the Brevoortia tyrannus all sem- 

 blance of regularity disappears, and it is impossible to count either lon- 

 gitudinal or vertical rows. The number of scales is enormously increased, 

 apparently by the growth of additional scales in the interspaces between 

 those already arranged in regular order. The number of scales in the 

 longitudinal rows is from GO or 70 in young individuals, to 110 in adults j 

 in the vertical rows, 25 or 26. 



10. — Internal organs. 



Gillstrainers. 



51. There are no vestiges of teeth in the mouths of any members of 

 the genus Brevoortia. These fish do not feed upon living animals, and 

 teeth would be useless to them. Their place is supplied by an ar- 

 rangement of setiform appendages, attached to the anterior edges of the 

 arches supporting the gills. These are closely set, flexible, and in 

 Brevoortia tyrannus about 170 iu number on each side of each of the 

 arches. There being thus four rows upon each side of the mouth, there 

 must be in the mouth of the menhaden from 1,400 to 1,500 of these 

 thread-like bristles, from one- third to three quarters of an inch long. 

 These may be so adjusted that they form a very effective strainer, much 

 resembling that of the right whale. This strainer is much finer and 

 more effective than in the whale, the number of bristles being much 

 more numerous than are the plates of baleen in the mouth of the right 

 whale. The uses to which this strainer is applied will be discussed 

 beloWj in paragraphs 119-125. 



The accessory hranchial organ. 



52. There is also a curious accessorj" branchial organ, situated be- 

 tween the top of the fourth branchial arch and the base of the skull. 

 This has been described from dissections of a fish identified as Clupano- 

 don aureus, Spix, in a paper by Prof. Joseph Hyrtl,* cited in full in the 



Bibliography. 



The alimentary canal. 



53. The alimentary canal in the menhaden is peculiar. The pharynx 

 is continued, in a straight canal, to the point of the siphonal stomach, 

 which extends backward nearly to the posterior extremity of the in- 

 testinal cavity, then turning at an acute angle returns nearly to the 



* Deukschriften Kaiserl. Akad. Wiss. Mat.-Nat. Class, vol. x, 1855, p. 49. 



