GLOBE-FISHES. 429 



continuous. The elongate tail terminates in a forked fin ; and the body is invested 

 with spiny bony plates, which do not overlap one another. The single species, which 

 may attain a length of 20 inches, ranges over the Indian and Malayan seas, and is of 

 a general brown colour, with a spot of variable colour on the sac, and the fins yellow. 

 The essential characteristics of the globe-fishes, which form the 

 second subfamily, are that the tail and its fin are distinct and well 

 developed, and that a portion of the oesophagus is highly distensible and capable of 

 being inflated with air. All the globe-fishes, or, as they are sometimes called, sea- 

 hedgehogs, are easily recognised by the short and cylindrical or rounded form of 

 the body ; which is generally covered with a scaleless skin bearing a number of 

 spines of 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 coloured 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 

 coloured. One member of the genus inhabits the rivers of Brazil, and a second 

 those of West Africa 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 globe-fish (Diodon hystrix) is shown 

 in the lower figure of the coloured 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 edge 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 globe-fish (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 globe-fishes 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-downwards, 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 distention is, 

 therefore, evidently for the purpose of defence ; 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 desirous 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. 



