302 ON POISONOUS FISHES AND FISH-POISONS. 



mackerel tribe, the family of fishes to which the tunny belongs. We have 

 enumerated some of the instances of scomberoid fishes that are pernicious. 

 We have mentioned the bonito, and naming some of the caranxes and 

 jacks, we have included the Corypheena dolphin, the king-fish, and the 

 Spanish mackerel among them. 



Every one has remarked the lateral line that extends along the scaling 

 of fishes from the gills to the tail, either interrupting or dividing the dormal 

 imbrication. This Line has a relation with the mucus that lubricates the 

 skin, — " quelque appareil secretaire qui en suit la longueur." This lateral 

 line is especially distinct in the tunny fish. Along it there occurs a 

 peculiar reddening of the flesh, deeper than in any other part of the 

 body. A number of little tubes forming pores start off from it ; each of 

 these little tubes has a bundle of nerves. There is something very similar 

 to this in the carp. 



In addition to this peculiarity of red flesh in the lateral line of the 

 tunny, one of the most distinguished of the mackerels, we have to consider 

 the non-existence of that reservoir for air known as the swimming-bladder, 

 placed beneath the spine. The gas in this bladder, whether it be nitrogen 

 or oxygen, is a product of secretion. " The air-sac is most developed in 

 species which frequent or feed at the surface of the water, and is least 

 developed or wanting in those which lie at the bottom, or burrow in mud ; 

 its secretion contains a larger proportion of oxygen in the powerful 

 predaceous fishes of deep seas, and nitrogen predominates in the feebler 

 species which frequent shores and shallow waters. Being developed, like 

 the lungs of higher animals, from the alimentary canal, the air-sac of 

 fishes generally communicates with the oesophagus or stomach, by means 

 of a short trachea or ductus pneumaticus : in some, however, this tracheal 

 communication becomes completely obliterated, and the sac remains an 

 isolated, closed cavity, filled with its gaseous secretion." (Outlines of Com- 

 parative Anatomy, by Robert E. Grant, M.D., chap, iv., 5th sec.) 



Cuvier very justly observes that whatever opinion may be entertained 

 relative to the use of the air-bladder, it is difficult to explain how so con- 

 siderable an organ has been denied to so many fishes as occur in our re- 

 searches ; not only to those which ordinarily remain quiet at the bottom of 

 the water, as rays and flat-fishes, but to many others that apparently yield 

 to none in the rapidity or facility of their movements. The presence or 

 the absence of the swimming-bladder has, however, no accordance with 

 conformation, or no relationship with it. A species nearly approaching 

 the common mackerel, the Scomber pneumatophorus, is provided with this 

 organ, and bears a name from having it, as a distinction: the Thynnus vul- 

 garis is without it, while the Thynnus brachiopterus has it, though small. 

 It is wanting in the Pelamys sarda, one of the bonitos, and in the Auxis vul- 

 garis, another, and occurs in the remoter scomberoid, the Tricliiurus leptu- 

 rus, the cutlass-fish. It does not exist in the Coryphaena dolphin, but is 

 largely found in the caranxes or jacks. It is difficult to trace the effects of 

 these differences in fishes of the mackerel family. Though the air-bladder 



