Ord. 2. LEIOMETOPA.—Nauplius without frontal horns. (Copepoda, without _Achtheus,_ etc., Phyllopoda, _Penëus._) Sub-class II. HEMISCHISTA.—Segmentation not complete. A. Nototropa.—Embryo bent upwards. Ord. 3. _Protura._—The tail is first formed. (_Mysis._) Ord. 3. _Saccomorpha._—A maggot-like larva-skin is first formed. (_Isopoda._) B. Gasterotropa.—Embryo bent ventrally. Ord. 5. _Zoëogona._—Full number of limbs not produced in the egg. Zoëa-brood. (The majority of the Podophthalmata.) Ord. 6. _Ametabola._—Full number of limbs produced in the egg. (_Astacus, Gecarcinus, Amphipoda_ less _Hyperia ?_) This sample may suffice. The farther we go into details in this direction, the more brilliantly, as may easily be imagined, does the naturalness of such an arrangement as this force itself upon us. All things considered, we may apply the judgment which Agassiz pronounced upon Darwin’s theory, with far greater justice to the propositions just examined:—“No theory,” says he, “however plausible it may be, can be admitted in science, unless it is supported by facts.” [1] “A plan fully matured in the beginning and undeviatingly pursued;” or “In the beginning His plan was formed and from it He has never swerved in any particular” (Agassiz and Gould, ‘Principles of Zoology’). [2] “Deos escrive direito em linhas tortas.” To read this remarkable writing we need the spectacles of Faith, which seldom suit eyes accustomed to the Microscope. [3] ‘Principles of Zoology’ Part I. Comparative Physiology. By Louis Agassiz and A.A. Gould. Revised Edition. Boston, 1856. [4] Agassiz’ own views have lately become essentially different, so far as can be made out from Rud. Wagner’s notice of his ‘Essay on Classification.’ Agassiz himself does not attempt any criticism of the above cited older views, which, however, are still widely diffused. With his recent conception I am unfortunately acquainted only from R. Wagner’s somewhat confused report, and have therefore thought it better not to attempt any critical remarks upon it. CHAPTER XI. ON THE PROGRESS OF EVOLUTION. From this scarcely unavoidable but unsatisfactory side-glance upon the old school, which looks down with so great an air of superiority upon Darwin's “intellectual dream” and the “giddy enthusiasm” of its friends, I turn to the more congenial task of considering the developmental history of the Crustacea from the point of view of the Darwinian theory. Darwin himself, in the thirteenth chapter of his book, has already discussed the conclusions derived from his hypotheses in the domain of developmental history. For a more detailed application of them, however, it is necessary in the first place to trace these general conclusions a little further than he has there done.