56 
mud-banks of the Ganges, while its armoured portion was extended 
in search of food. 
From such examples we proceeded to the Ostractonide and 
Syngnathide, the Box and Pipe Fishes, which were covered with less 
dense bony plates, but which, in the former, were anchylosed so firmly 
as to be immovable except at the tail and fins. Thence to the Stur- 
geons, covered with broad shield-like plates, and on to the Sharks, 
Rays, and Skates, having their outer surfaces studded with spines and 
tubercles. The plates of the Sturgeon were covered with enamel, and 
were of a true omy structure with lacunz and canaliculi, while the spines 
from the Skate and Shark were Zoo¢h-dike in structure and hardness, 
and sometimes were, both in external and internal character, so like 
teeth that they might be mistaken for them. Associated with these 
external characters we invariably found an imperfectly-developed or 
cartilaginous skeleton. 
In the Osseous fishes, with which we were most familiar, the dony 
skeleton was accompanied by an outer covering of horny and elastic 
scales, beautifully and regularly imbricated, smooth, and impervious 
to water, and arranged so as to offer the least possible resistance to the 
movements of the fish in the dense medium it inhabited. 
In the Ctenoid fishes, such as the Sole, Basse, Perch, &c., the 
comb-like scales projected through the epidermis; but in Cycloid 
fishes, such as the Carp, Herring, Salmon, &c., they were com- 
pletely covered by it. In the Eel—a Cycloid fish—the scales were so 
deeply buried in the slimy skin as to escape general observation. 
Scales were true cuticular appendages, each imbedded in a 
separate sac or fold of the cutis, to which its under surface was ad- 
herent, while externally it was covered with epidermis and pigment 
cells. Scales were, in fact, mostly made up of layers of horny matter, 
secreted by the cutis in the same manner as the shells of Molluscs ; 
the smaller and more superficial layers being first formed, while the 
larger and more recent lay beneath them and were in contact with the 
living skin. The radiating lines seen on most scales seemed, at first 
sight, inconsistent with the explanation just given of their mode of 
growth. It was, however, supposed that, after a few layers had been 
formed, they began to split by contraction in becoming solid, and that 
the lower layers were formed after each upper one had hardened, 
exceeding it a little in size and filling up the slit, giving rise to both 
radiating and concentric lines. 
In the scales of the Carp the outer layers were as just described, 
