GLOBE-FISHES. 687 



a distinct genus, Enneodon, has been described from Monte 

 Postale. The Gymnodonts may be divided into three groups : 



A. Triodontina. — Tail rather long, with a separate caudal 

 fin. Abdomen dilatable into a very large, compressed, pendent 

 sac, the lower part of which is merely a flap of skin, into which 

 the air does not penetrate, the sac being capable of being ex- 

 panded by the very long pelvic bone. The upper jaw divided by 

 a median suture, the lower simple. 



A single genus and species {Triodon hur sarins) from the 

 Indian Ocean. 



B. Tetrodontina. — Tail and 'caudal fin distinct. Part of the 

 oesophagus much distensible, and capable of being filled with air. 

 No pelvic bone. 



" Globe-fishes " have a short, thick, cylindrical body, with 

 well developed fins. It is covered with thick scaleless skin, 

 in which, however, spines are imbedded of various sizes. The 

 spines are very small, and but. partially distributed over the 

 body in some species, whilst in others they are very large, 

 and occupy equally every part of the body. These fishes 

 have the power of inflating their body by filling their disten- 

 sible oesophagus with air, and thus assume a more or less 

 globular form. The skin is, then, stretched to its utmost extent, 

 and the spines protrude and form a more or less formidable 

 defensive armour, as in a. hedgehog; therefore they are fre- 

 quently called " Sea-hedgehogs." A fish thus blown out turns 

 over and floats belly upwards, driving before the wind and 

 waves. However, it is probable that the spines are, a protec- 

 tion not only when the fish is on the surface and able to take 

 in air, but also when it is- under water. Some Diodonts, 

 at any rate, are able to erect the spines about the head by 

 means of cutaneous muscles ; and, perhaps, all fill their 

 stomach with water instead of air, for the same purpose and 

 with the same effect. In some Diodonts the spines are fixed, 

 erect, not movable. The Gymnodonts generally, when taken. 



