In the month of January, 187-, M. Hollydorf was selected to conduct an exploring corps of the R. H. B. Society to the head waters of the Paraguay and its tributaries, for the purpose of observing the habits and classifying the different species of animalcular life native to the trees and plants appertaining to those regions. The Royal Society had supplied him with able assistants, and the most complete set of instruments ever constructed for botanical or other research in the fields of natural science. Among the instruments of recent invention, was one of Lutsenwitz’s solar reflecting microscopes, especially designed for field explorations. This was of the highest concentrated power yet attempted by that artist,—the intensity of its magnifying capacity being capable of showing the facial contortions of the most minute animalculæ. Attached to the focal platform was one of Phlegmonhau’s highest grade of responsive tympanums, with reflecting auricle for magnifying the articulation of sound. The corps arrived at Montevideo on the first day of April, and was fortunate in finding a small trading steamer, under neutral colors, ready with quick despatch for a barter voyage up the Paraguay and its tributaries, without a specified port of final destination. The captain was sole owner, and proved to be a man of rare intelligence, which had been cultivated by travel and study. To his love of adventure was added a strong amateur predisposition for the pursuits of natural history. These qualifications led to a speedy agreement, with conditional arrangements for a charter of the steamer open to variations suited to the requirements of the corps. * * * * *