entifically interpreted save on the hypothesis of a common ultimate origin for mammals, birds, reptiles, and fishes. 3. What is the meaning of such facts as the homologies which exist between corresponding parts of organisms constructed on the same type? Why does the black salamander retain fully-developed gills which he never uses, and what is the significance of rudimentary and aborted organs in general? Again I say, we do not want to hear about "uniformity of design" and "reminiscences of a plan," and so on, but we wish to know how this state of things was physically brought about, save by community of descent. 4. Why is it that the facts of geological succession and geographical distribution so clearly indicate community of descent, unless there has actually been community of descent? Why have marsupials in Australia followed after other marsupials, and edentata in South America followed after other edentata, with such remarkable regularity, unless the bond which unites present with past ages be the well-known, the only known, and the only imaginable bond of physical generation? Why are the fauna and flora of each geologic epoch in general intermediate in character between the flora and fauna of the epochs immediately preceding and succeeding? And, 5. What are we to do with the great fact of extinction if we reject Mr. Darwin's explanations? When a race is extinguished, is it because of a universal deluge, or because of the "free manifestations of an intelligent mind?" For surely Prof. Agassiz will not attribute such a solemn result to such ignoble causes as insufficiency of food or any other of the thousand causes, "blindly mechanical," which conspire to make a species succumb in the struggle for life.
And here the phrase, "struggle for life," reminds me of yet another difficult task which Prof. Agassiz will have before him when he comes to undertake the refutation of Darwinism in earnest. He will have to explain away the enormous multitude of facts which show that there is a struggle for life in which the fittest survive; or he will at any rate have to show in what imaginable way an organic type can remain constant in all its features through countless ages under the influence of such circumstances, unless by taking into the account the Darwinian interpretation of persistent types offered by Prof. Huxley.
But I will desist from further enumeration of the difficulties which surround this task which Prof. Agassiz has not undertaken, and is not likely ever to undertake. For the direct grappling with that complicated array of theorems which the genius of such men as Darwin and Spencer and their companions has established on a firm basis of observation and deduction, Prof. Agassiz seems in these lectures hardly better qualified than a child is qualified for improving the methods of the integral calculus. These questions have begun to occupy earnest thinkers since the period when his mind acquired that rigidity which prevents the revising of one's opinions. The marvellous flexibility of thought with which Sir Charles Lyell so gracefully abandoned his an-
