THE GLOBEFISHES AND SUNFISHES 2801 



variable size. When these spines are of large size, they are spread uniformly over 

 the whole body, but when small they are partial in their distribution. These fishes 

 are divided into two groups, according to the nature of the dental plates. In the 

 first, or small-spined group, as typified by the genus Tetrodon, of which a species 

 is represented in the lower figure of the colored plate, the dental plate of each jaw 

 is divided by a median suture, and the spines are frequently very small, and may be 

 even altogether absent; many of the species being very brilliantly colored. One 

 member of the genus inhabits the rivers of Brazil, and a second those of West Af- 

 rica and the Nile, while a small form is found in the brackish-water estuaries of 

 India. According to Day, the flesh of some of the species is poisonous, while that 

 of other kinds is eaten by the Andamanese and Burmese. In the second group, of 

 which the porcupine globefish (Diodon hystrix] is shown in the lower figure of the 

 colored illustration, the dental plates in the jaws are undivided, and the spines are 

 large and frequently erectile. In addition to the undivided dental plates on the 

 edges of the jaws, in the members of this group there is another crushing plate in 

 the middle of the palate, opposed by a similar one in a corresponding position in the 

 lower jaw; these plates being divided by a median suture and from their laminated 

 structure forming most admirable triturating instruments. The porcupine globe- 

 fish, which may measure fully a couple of feet in length, is distributed over both 

 the Atlantic and Indo-Pacific Oceans, where it is accompanied by the smaller spotted 

 globefish (D. maculatus). Fossil diodons have been discovered in the Miocene 

 strata of Malta and Sicily, as well as in the middle Eocene of Monte Bolca, and in 

 other Eocene beds on the coasts of Algeria and Arakan; while an extinct genus has 

 also been recorded from the Italian Eocene. In their normal state the globefishes 

 have rather elongated cylindrical bodies, but they are able to assume a globular 

 form by swallowing air, which passes into the oesophagus and blows out the whole 

 animal like a balloon, with the spines standing out at right angles from the tense 

 skin. In this condition the fish naturally floats back downward, and it is then 

 driven to and fro on the ocean surface by waves and currents in a perfectly helpless 

 condition; although the bristling spines render it perfectly safe from all attack. 

 The distension is, therefore, evidently for the purpose of defense; and it has 

 been suggested that when swimming below the surface these fishes may inflate 

 themselves in a similar manner by swallowing water instead of air. When desir- 

 ous of returning to its normal condition, the fish expels the air from the oesophagus 

 through the mouth and gill openings; a loud, hissing noise being produced by the 

 expulsion. 



The gigantic sunfishes ( Orthagoriscus) , which are pelagic forms 

 distributed throughout the whole of the temperate and tropical seas, 

 alone represents the third subfamily, and are distinguished by the extremely 

 short and truncated tail, the confluence of all the median fins, and the short and 

 highly compressed body, the dental plates of the jaws being undivided. The skin 

 is either rough or smoothly tesselated, and incapable of distension with air; there 

 are no pelvic fins; the air bladder is wanting; and there is an accessory opercular 

 gill. As in the globefishes, there are no pelvic bones in the skeleton, and the ver- 

 tebral column is remarkable for its extreme shortness, there being only seventeen 

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