_September 15th._—For the last two or three days we have been holding frequent discussions as to the best disposition of our forces after reaching Tabatinga;—a source of great anxiety to Mr. Agassiz, the time we have to spend being so short, and the subjects of investigation so various and so important. Should he give up the idea of continuing, in person, his study of the fishes in the upper Amazons, leaving only some parties to make collections, and going himself into Peru, to visit at least the first spur of the Andes, with the purpose of ascertaining whether any vestiges of glaciers are to be found in the valleys, and also of making a collection of fishes from the mountain streams; or should he renounce the journey into Peru for the present, and, making a station somewhere in this region for the next month or two, complete, as far as may be, his investigation of the distribution and development of fishes in the Solimoens? Had the result of the Peruvian journey been more certain, the decision would have been easier; but it is more than likely that the torrential rains of this latitude have decomposed the surface and swept away all traces of glaciers, if they ever existed at so low a level. To go on, therefore, seemed a little like giving up a certain for an uncertain result. Earnestly desirous of making the best use of his time and opportunities here, this doubt has disturbed Mr. Agassiz’s waking and sleeping thoughts for several days past. Yesterday morning, at Teffé, a most unexpected adviser appeared in the midst of our council of war. Insignificant in size, this individual, nevertheless, brought great weight to the decision. The intruder was a small fish with his mouth full of young ones. The practical plea was irresistible,—embryology carried the day. A chance of investigating so extraordinary a process of development, not only in this species but in several others said to rear their young in the same fashion, was not to be thrown away; and, besides, there was the prospect of making a collection and a series of colored drawings, from the life, of the immense variety of fishes in the river and lake of Teffé, and perhaps of studying the embryology of the turtles and alligators in their breeding season. Mr. Agassiz, therefore, decides to return to Teffé with his artist and two or three other assistants, and to make a station there for a month at least, leaving Mr. Bourget, with our Indian fisherman, at Tabatinga to collect in that region, and sending Mr. James and Mr. Talisman to the river Putumayo, or Iça, and afterwards to the Hyutahy for the same purpose. This dispersion of parties to collect simultaneously in different areas, divided from each other by considerable distances, will show how the fishes are distributed, and whether their combinations differ in these localities as they have been found to do in the Lower Amazons.