-Young Guinea-worm, showing Mouth, Tail, and section of Body 153 33.-Gregarinæ of Nemertes ... 34.-Sac with Psorospermiæ from Sepia officinalis 35.-Stylorhynchus oligacanthus from Dragon-fly ... 36.-Horse-fly, showing also Anterior and Posterior Extremity 37.-Macaco Worm ... 41.-Monostomum verrucosum-Sporocyst with Cercaria 44.-Ditto, ciliated Embryo and young Cercariæ PAGE ... ... ... 51.-Tape-worm (Tænia solium), showing Scolex and Proglottides 214 ... ... ... ... 214 ... ... ... 219 61. Tænia variabilis from Snipe 62.-Ditto, more highly magnified 63.-Tetrarhynchus appendiculatus from the Plaice... 67.-Ascaris lumbricoides; also Head, Tail, and Body ... 240 241 ... ... ... 73.-Sac with Psorospermiæ from Sepia officinalis 74.-Gregarinæ from Nemertes Gesseriensis 75.-Stylorhynchus oligacanthus 76.-Dicyema Krohnii from Sepia officinalis 30 311 ... 32. 252 80.-Cochineal Insects, male 81.-Ditto, female 82.-Aphis 263 264 264 ... 83.-Rose Aphis, male and female ... ... ... INTRODUCTION. "The edifice of the world is only sustained by the impulses of hunger and love."-SCHILLER. In that great drama which we call Nature, each animal plays its especial part, and He who has adjusted and regulated everything in its due order and proportion, watches with as much care over the preservation of the most repulsive insect, as over the young brood of the most brilliant bird. Each, as it comes into the world, thoroughly knows its part, and plays it the better because it is more free to obey the dictates of its instinct. There presides over this great drama of life a law as harmonious as that which regulates the movements of the heavenly bodies; and if death carries off from the scene every hour myriads of living creatures, each hour life causes new legions to rise up in order to replace them. It is a whirlwind of being, a chain without end. This is now more fully known; whatever the animal may be, whether that which occupies the highest or the lowest place in the scale of creation, it consumes water and carbon, and albumen sustains its vital force. Therefore, the Hand which has brought the world. out of chaos, has varied the nature of this food; it has proportioned this universal nourishment to the necessities and the peculiar organization of the various species which have to derive from it the power of motion and the continuance of their lives. The study whose aim is to make us acquainted with the kind of food adapted to each animal constitutes an interesting branch of Natural History. The bill of fare of every animal is written beforehand in indelible characters on each specific type; and these characters are less difficult for the naturalist to decipher than are palimpsests for the archæologist. Under the form of bones or scales, of feathers or shells, they show themselves in the digestive organs. It is by paying, not domiciliary, but stomachic visits, that we must be initiated into the details of this domestic economy. The bill of fare of fossil animals, though written in characters less distinct and complete, can still be very frequently read in the substance of their coprolites. We do not despair even to find some day the fishes and the crustaceans which were chased by the plesiosaurs and the ichthyosaurs, and to discover some parasitic worms which had entered with them into the convolutions of the intestines of the saurians. Naturalists have not always studied with sufficient care the correspondence which exists between the animal and its food, although it supplies the student with information of a very valuable kind. In fact, every organized body, whether conferva or moss, insect or mammal, becomes the prey of some animal; every organic substance, sap or blood, horn or feather, flesh or bone, disappears under the teeth of some one or other of these; and to each kind of débris correspond the instruments suitable for its assimilation. These primary relations between living beings and their alimentary regimen call forth the activity of every species. We find, on closer examination, more than one analogy between the animal world and human society; and without much careful scrutiny, we may say that there is no social position which has not (if I may dare to use the expression) its counterpart among the lower animals. The greater part of these live peaceably on the fruit of their labour, and carry on a trade by which they gain their livelihood; but by the side of these honest workers we find also some miserable wretches who cannot do without the assistance of their neighbours, and who establish themselves, some as parasites in their organs, others as uninvited guests, by the side of the booty which they have gained. Some years ago, one of our learned and ingenious colleagues at the University of Utrecht, Professor Harting, wrote a charming book on the industry of animals, and demonstrated that almost every trade is known in the animal kingdom. We find among them miners, masons, carpenters, paper manufacturers, weavers, and we may even say lace-makers, all of whom work first for themselves, and afterwards for their progeny. Some dig the earth, construct and support vaults, clear away useless earth, and consolidate their works, like miners; others build huts or palaces according to all the rules of architecture; others know intuitively all the secrets of the manufacturers of paper, cardboard, woollen stuffs or |