36 A JOURNEY IN BRAZIL. 



the lower ones, in which it acquires a special final structure ; 

 giving place to lungs in the higher ones before they reach 

 their adult condition. From this time forward not only the 

 class characters, but those of the family, begin to be dis- 

 tinguished. I will show you to-day how we may improve 

 the classification of fishes by studying their embryology. 

 Take, for instance, the family of Cods in its widest ac- 

 ceptation. It consists of several genera, among which are 

 the Cod proper, the Cusk, and the Brotula. Naturalists 

 may differ in their estimation of the relative rank of these 

 genera, and even with reference to their affinity, but the 

 embryology of the Cod seems to me to give the natural 

 scale. In its early condition the Cod has the continuous fin 

 of the Brotula, next the dorsal and caudal fins become dis- 

 tinct, as in the Cusk, and lastly the final individualization of 

 the fins takes place, and they break up into the three dorsals 

 and two anals of the Cod. Thus the Brotula represents the 

 infantile condition of the Cod, and of course stands lowest, 

 while the Cusk has its natural position between the two. 

 There are other genera belonging to this family, as, for in- 

 stance, the Lota or fresh-water Cusk and the Hake, the rela- 

 tive position of which may be determined by further embryo- 

 logical studies. I had an opportunity of observing 'some- 

 thing in the development of the Hake which throws some 

 light on the relation of the Ophidini to the Cod family, though 

 thus far they have been associated with the Eel. The little 

 embryonic Hake on which I made my investigation was about 

 an inch and a half in length ; it was much more slender 

 and elongated in proportion to its thickness than any of the 

 family of Cods in their adult condition, and had a continu- 

 ous fin all around the body. Although the structural rela- 

 tions of the Eels are not fully understood, some of them, at 



