If we admit that the other orders of insects, the Lepidoptera, the Hemiptera, the Hymenoptera, the Neuroptera, the Orthoptera, the Diptera, the Strepsiptera, comprise, taken altogether, at least the same number of species as the Coleoptera alone, we shall gain, for the class of insects, a total of 200,000. And we shall certainly keep within the truth if we assign the same number of species to the Annelida, the Crustacea, the Arachnida, the Myriapoda, and the Monomorpha, to which, with some modification, we may apply the remarks already called forth by the Coleoptera. Let us recapitulate. The four classes of _Vertebrate Animals_ include approximatively:-- 1,600 species Mammals. 5,000 " Birds. 2,000 " Reptiles. 12,000 " Fishes. ------ 20,600 If we add to these 20,600 species of Vertebrate Animals, 200,000 species of Articulata, and 22,000 Mollusca (a minimum), we shall have a total of 242,600. But to complete the grand whole of beings "who grow, and live, and feel" (the definition of animals laid down by Linnæus), we must add the Intestinal Worms, the Echinodermata, the Acalephæ (or Sea-nettles), and the Polypes. The history of these singular creatures, which apparently form the transition between the animal and vegetable kingdom, and have thence been designated _Zoophytes_, leaves much, very much, to be desired before it will be possible to indicate, even approximatively, the number of their species. * * * * * And, finally, what shall we say of the Infusoria? These microscopic forms of life seem, by their extreme multiplicity, to animate all nature. It is in studying these that the inquirer needs to be constantly on his guard, that he may not mistake transitory conditions--or larvæ--for actual species, and it behoves him to understand thoroughly the difficult delimitation of specific characters. It would be far easier to ascertain the exact number of human beings who at present people the terrestrial surface, than to fix the total of the species of Infusoria now in existence; assuredly it exceeds 250,000. What an infinite variety of design is here! What a picture it presents of the inexhaustibility of the Creative Mind! * * * * * Add, then,--let us say, in conclusion,--to this last great total the aggregate of the Vertebrates, the Articulates, and the Molluscs, and for our grand whole we have a minimum of _half a million_ of ANIMAL SPECIES! This is the very figure, observe, at which we arrived as representing the lowest limit of the totality of VEGETABLE SPECIES, living and moving, flourishing, and dying, and reproducing, on the surface of the globe. We leave the reader to meditate--as meditate he surely must--on the sublime thoughts, the overpowering ideas of Power and Wisdom which these considerations suggest. WHAT IS CHLOROPHYLL?