Always yours, L. AGASSIZ. Footnote 70: We found that this information was incorrect, at least for some species, as will be seen hereafter. I let the statement stand in the text, however, as an instance of the difficulty one has in getting correct facts, and the danger of trusting to the observations even of people who mean to tell the real truth. No doubt some of these Acaras do occasionally deposit their young in the sand, and continue a certain care of them till they are able to shift for themselves. But the story of the fisherman was one of those half truths as likely to mislead, as if it had been wholly false. I will add here a few details concerning these Acaras, a name applied by the natives to all the oval-shaped Chromides. The species which lay their eggs in the sand belong to the genera Hydrogonus and Chætobranchus. Like the North American Pomotis, they build a kind of flat nest in the sand or mud, in which they deposit their eggs, hovering over them until the young are hatched. The species which carry their young in the mouth belong to several genera, formerly all included under the name of Geophagus by Heckel. I could not ascertain how the eggs are brought into the mouth, but the change must take place soon after they are laid, for I have found in that position eggs in which the embryo had just begun its development as well as those in a more advanced stage of growth. Occasionally, instead of eggs, I have found the cavity of the gills, as also the space enclosed by the branchiostegal membrane, filled with a brood of young already hatched. The eggs before hatching are always found in the same part of the mouth, namely, in the upper part of the branchial arches, protected or held together by a special lobe or valve formed of the upper pharyngeals. The cavity thus occupied by the eggs corresponds exactly to the labyrinth of that curious family of fishes inhabiting the East Indian Ocean, called Labyrinthici by Cuvier. This circumstance induces me to believe that the branchial labyrinth of the eastern fishes may be a breeding pouch, like that of our Chromides, and not simply a respiratory apparatus for retaining water. In the Amazonian fish a very sensitive network of nerves spreads over this marsupial pouch, the principal stem of which arises from a special nervous ganglion, back of the cerebellum, in the medulla oblongata. This region of the central nervous system is strangely developed in different families of fishes, and sends out nerves performing very varied functions. From it arise, normally, the nerves of movement and sensation about the face; it also provides the organs of breathing, the upper part of the alimentary canal, the throat and the stomach. In the electric fishes the great nerves