6 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 
