222 A JOURNEY IN BRAZIL. 



for the younjr prevails more or less in all the family of 

 Acara. They are not all born there, however ; some lay 

 their eggs in the sand, and, hovering over their nest, 

 take up the little ones in their mouth, when they are 

 hatched. The fishermen also add, that these fish do not 

 always keep their young in the mouth, but leave them 

 sometimes in the nest, taking them up only on the approach 

 of danger.* 



* 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 

 Chcetobranchus. 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 

 Geophngus 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 develop- 

 ment as well as those in a more advanced stage of growth. Occasionally, in- 

 stead 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 oc- 

 cupied by the eggs corresponds exactly to the labyrinth of that curious family 

 of fishes inhabiting the East Indian Ocean, called Lahyrinthici 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 sen- 

 sitive 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 



