An exceptional property in fishes and in birds for the most
part is the being furnished with gut-appendages or caeca. Birds have
them low down and few in number. Fishes have them high up about the
stomach, and sometimes numerous, as in the goby, the galeos, the
perch, the scorpaena, the citharus, the red mullet, and the sparus;
the cestreus or grey mullet has several of them on one side of the
belly, and on the other side only one. Some fish possess these
appendages but only in small numbers, as the hepatus and the
glaucus; and, by the way, they are few also in the dorado. These
fishes differ also from one another within the same species, for in
the dorado one individual has many and another few. Some fishes are
entirely without the part, as the majority of the selachians. As for
all the rest, some of them have a few and some a great many. And in
all cases where the gut-appendages are found in fish, they are found
close up to the stomach.