them. The minds of zoölogists were not prepared in his time to receive his ideas, and he had not the happy faculty of hitting upon that clear and precise method of statement that imposes itself and makes itself accepted by all. For a reformer to secure a following, his idea should be defined with dazzling clearness and precision, and achieve mastery by virtue of its seductive force. Darwin's exposition of the universal and constant struggle for existence, ending in the selection and survival of the victor, was so true and clear as to lead all readers into accord with it. Cuvier, they said, could reconstruct the whole of an extinct animal from a single bone. The thought spoke to the imagination of the masses; and when he laid down the principle that in an organism, as in an equation, the known terms may be made to give an unknown one, he commanded the admiration of a whole generation. Linnæus, who at a stroke reached the reform science was aspiring after, to rid itself of nonsense in nomenclature, and who found names to fit the occasion, became the tyrant of natural history. It was not possible for Lamarck to realize a similar success; and a comparison of his arguments with those which Darwin brings in support of the doctrine of changes in the forms of animals, and a reference to the epoch in which he wrote, will show why his ideas had to wait for the revelations of the English naturalist before they could be recovered from oblivion.
In view of the surprising discoveries to which the continuous study of the evolution of the lower animals has led, and of the direction of zoölogy under the influence of transformism into new ways, it is impossible not to recognize that experiment alone fulfills the requirements of the moment. It is only through experiment that the great questions of natural philosophy can be answered; that the discussions raised by clashing convictions, hazardous assertions, so-called philosophical doctrines, and venturesome syntheses too often lacking substantial bases, can be justly appreciated or solidly established.
The citation of a few instances will illustrate this assertion. Every one has noticed the gall-nuts on oak-trees, excrescent tumors produced by parasitical insects—the Cynips—which lay their eggs in the mother plant by the aid of a gimlet-shaped ovipositor. The young insect finds within this swelling all that it needs to support life, and quietly in it reaches complete development; and it can easily be caught as it issues from its prison. Entomologists have catalogued a large number of species and genera belonging to the family. In doing thus, they have followed pure and descriptive zoölogy, as it was in the times of Linnæus and Cuvier. Now, it has been found, after watching the evolution of these parasites, that all the genera and species have to be revised. Thus, for example, we find on the superficial roots of an oak-tree galls
