The lecture concluded with some advice as to observing and recording the metamorphoses of insects. “Though much has been written on the societies of ants and other like communities in Brazil, the accounts of different naturalists do not agree. It would be well to collect the larvæ of a great many insects, and try to raise them; but as this will be difficult and often impossible in travelling, we must at least get the nests of ants, bees, wasps, and the like, in order to ascertain all we can respecting their communities. When these are not too large it is easy to secure them by slipping a bag over them, thus taking the whole settlement captive. It may then be preserved by dipping into alcohol, and examined at leisure, so as to ascertain the number and nature of the individuals contained in it, and learn something at least of their habits. Nor let us neglect the domestic establishments of spiders. There is an immense variety of spiders in South America, and a great difference in their webs. It would be well to preserve these on sheets of paper, to make drawings of them, and examine their threads microscopically.” _April 21st._—Yesterday Mr. Agassiz gave his closing lecture, knowing that to-day all would be occupied with preparations for landing. He gave a little history of Steenstrup and Sars, and showed the influence their embryological investigations have had in reforming classification, and also their direct bearing upon the question of the origin of species. To these investigators science owes the discovery of the so-called “alternate generations,” in which the Hydroid, either by budding or by the breaking up of its own body, gives rise to numerous jelly-fishes; these lay eggs which produce Hydroids again, and the Hydroids renew the process as before.[14] “These results are but recently added to the annals of science, and are not yet very extensively known in the community; but when the facts are more fully understood, they cannot fail to affect the fundamental principles of zoölogy. I have been astonished to see how little weight Darwin himself gives to this series of transformations; he hardly alludes to it, and yet it has a very direct bearing on his theory, since it shows that, however great the divergence from the starting-point in any process of development, it ever returns to the road of its normal destiny; the cycle may be wide, but the boundaries are as impassable as if it were narrower. However these processes of development may approach, or even cross each other, they never end in making any living being different from the one which gave it birth, though in reaching that point it may pass through phases resembling other animals.