THE PRIMARY TYPES OF FORM. lOQ 



of Bloch. The three fins of the tail, that is, the 

 hinder dorsal, the caudal, and the anal, if not united, as 

 in Cepola, Ophidium, Plotosus, Anarhichas, &c. are 

 only separated by a small interval, as in Physis, Mer- 

 langus, Blennius, &c. ; or the ventral fin only is exces- 

 sively long, as in all the genera and sub-genera of the 

 anguilliform division of the SiluridcB. In other genera, 

 the dorsal and caudal fins are obsolete; but the anal ex- 

 tends the entire length of the tail, which terminates in a 

 point. So far as our analysis has extended, it seems 

 that all these are but modifications of the anguilliform 

 structure. The ventral fins, which are universally 

 absent among the true Apodes, are sometimes wanting, 

 also, in their representatives, as in Ophidium, Anarhi- 

 chas, Ammodytes, &c.: usually, however, their slight de- 

 velopment marks the type we are now speaking of ; thus, 

 in the two families of the Blennid(JB and the Gadidce, 

 the typical genera have their fins composed only of two 

 rays, or, when the others are present, they merely exist 

 in a rudimentary state. The scales, again, frequently 

 present a pecuhar character : when present, they are 

 very small, often scarcely perceptible, and appear to be 

 inserted, as in the eels, beneath the cuticle : this is 

 seen in most of the GadidcF ; while in other anguilli- 

 form types, hke the BlennidfB, the body is slimy and 

 naked, either covered with an opaque skin, or semi- 

 transparent. The snout is always short and obtuse, 

 the mouth not extensible, and the teeth either very 

 small or none. Nearly the only mailed genus that 

 possesses the anguilliform shape is Folypterus j and 

 this, as we suspect, may probably belong to the order 

 Plectognathes. 



(98.) Having now stated some of the most preva- 

 lent analogies between the primary types and divisions 

 of fishes, and those of the warm-blooded Vertebrata, 

 we may exhibit the results in a more compact form by 

 placing these groups in three columns ; and it will then 

 be more distinctly seen in what way each is related 

 to the other by analogy. 



