The Tagus would again require an extensive exploration. In the first place a thorough collection of all the species found in the great estuary ought to be made with the view of ascertaining how far marine Atlantic species penetrate into the river basin; then one from Santarem, and another either from Talavera or Toledo or Aranjuez, and one from the head-waters in Guadalaxara, and another in Molina. The collections made at different stations ought carefully to be kept in distinct jars or kegs, with labels so secure that no confusion or mistake can arise. But the specimens collected at the same station may be put together in the same jar. These collections require, in fact, very little care. (Here some details about mode of putting up specimens, transportation, etc.) If the same person should collect upon different stations, either in the same or in different hydrographic basins, the similarity of the specimens should not be a reason for neglecting to preserve them. What is aimed at is not to secure a variety of species, but to learn in what localities the same species may occur again and again, and what are the localities which nourish different species, no matter whether these species are in themselves interesting or not, new to science or known for ages, whether valuable for the table or unfit to eat. The mere fact of their distribution is the point to be ascertained, and this, as you see, requires the most extensive collections, affording in themselves comparatively little interest, but likely to lead, by a proper discussion of the facts, to the most unexpected philosophical results. . .Do, please, what you can in this matter. Spain alone might give us the materials to solve the question of transmutation versus creation. I am going to make a similar appeal to my friends in Russia for materials from that country, including Siberia and Kamschatka. Our own rivers are not easily accessible now. Ever truly your friend, L. AGASSIZ. CHAPTER 20. 1863-1864: AGE 56-57. Correspondence with Dr. S.G. Howe. Bearing of the War on the Position of the Negro Race. Affection for Harvard College. Interest in her General Progress. Correspondence with Emerson concerning Harvard. Glacial Phenomena in Maine. AGASSIZ'S letters give little idea of the deep interest he felt in the war between North and South, and its probable issue with reference to the general policy of the nation, and especially to the relation between the black and white races. Although any judgment upon the accuracy of its conclusions would now be premature, the following correspondence between Agassiz and Dr. S. G. Howe is nevertheless worth considering, as showing how the problem presented itself to the philanthropist and the naturalist from their different stand-points. FROM DR. S.G. HOWE. PORTSMOUTH, August 3, 1863. MY DEAR AGASSIZ, You will learn by a glance at the inclosed circular the object of the commission of which I am a member.