PLECTOGNATHES. 231 



trals. The intestinal canal is ample, but without caeca*, and in almost 

 every instance there is a large natatory bladder. 



This order comprises two very natural families, characterized by the 

 mode in which their teeth are armed, namely, the Gymnodonfes and 

 Sceerodcrmes. 



The first family, that of the 



FAMILY I. 



GYMNODONTES (a), 



Has jaws, which, instead of teeth, are furnished with an ivory substance, 

 internally divided into laminae, which, in their aggregate, resemble a Par- 

 rot's bill, and which in fact consist of true teeth united, that succeed each 

 other as fast as they are destroyed by trituration -j~. Their opercula are 

 small, and there are five rays on each side, all of which are almost com- 

 pletely hidden. They live on Crustacea and sea-weed, their flesh is 

 generally mucous, and that of several species is considered poisonous, at 

 least in certain seasons. 



Two of the genera, the Tetraodons and Diodons, vulgarly called 

 Bloaters or Balls, have the faculty of swelling themselves up like a bal- 

 loon, by filling their stomach, or rather a sort of very thin and exten- 

 sible crop, which occupies the whole length of the abdomen, and adheres 

 closely to the peritoneum, a circumstance which has occasioned it to be 

 considered at one time as the peritoneum itself, and at another as a spe- 

 cies of omentum, with air. When thus inflated, they roll over, and float 

 on the surface, with the abdomen upwards, unable to direct their course; 

 but they are extremely well defended while in this position by the erec- 

 tion of the spines with which their skin is everywhere furnished J. Their 

 natatory bladder has two lobes, and their kidneys, which are placed very 

 high up, have been erroneously taken for lungs §. They have but three 

 branchiae on each sidejj, and when captured they produce a sound which 



* Bloch erroneously attributes caeca to genus Dodon. 



t See my Lecons d'Anat. Comp. vol. Ill, p. 125. 



J See Sir Geoflroy St. Hilaire, Poiss. d'Eg., in the great work on that country. A 

 similar disposition is observable in Chironectes. 



§ It is thus I explain the mistake of Schcepfer in the publications of the Nat. of 

 Berlin, VIII, 190, and that of Plumier, Schn. 513, and doubtless that of Garden, 

 Lin. Syst., Ed. XII, i, p. 348. As to the cellular organs mentioned by Broussonnet, 

 Ac. des Sc, 1780, last page, there is nothing to be found which resembles them. The 

 process of respiration in these fishes is similar in all things to that of others. 



|| An instance of this we have already seen in Lophius. 



(a) From the Greek, gumnos, naked, odous, a tooth. 



