630 H I C H place for undergoing that change to pupa which it will never make, must also have been observed by many. This is the work of Apanteles (or Microgaster) glomeratus, one of the Sraconidce, which in days past was a source of disquietude to naturalists, who believed that the life of the one defunct larva had transmigrated into the numerous smaller Hies reared from it. Ichneumon-flies which attack external feeders have a short ovipositor ; but those attached to wood-feeding insects have that organ of great length, for the purpose of reaching their concealed prey. Thus a species from Japan ( Bracon penetrator) has its ovipositor .nine times the length of the body ; and the large species of Rhyssa and Ephialtes, parasitic on Sirex and large wood- boring beetles in temperate Europe, have very long instru ments (with which when handled they will endeavour to sting, sometimes penetrating the skin), in order to get at their secreted victims. This length of ovipositor is, in the femnle of a species of Pelecinus, common in the boreal parts of North America in pine forests, replaced by an excessively attenuated development of abdomen, causing the insect to resemble a small dragon-fly, and fulfilling the same mechanical purpose. A common reddish-coloured species of Ophion (0. obsciinini), with a sabre-shaped abdomen, is noteworthy from the fact of its eggs being attached by stalks outside the body of the caterpillar of the puss-moth (Diranura vinida). Lepidopterists wishing to breed the latter cut off the eggs of the parasite with scissors. The larvae of the ichneumon-flies are white fleshy cylindrical footless grubs ; the majority of them spin silk cocoons before pupating, often in a mass (sometimes almost geometrically), and sometimes in layers of different colours and texture. The reader desirous of investigating more fully the structure and habits of this interesting family will, in addition to the older works of Gravenhorst, Esenbeck, Wesmael, and Haliday, find much matter in the recent writings of Brischke, Cresson, Provancher, Holmgren, Woldstedt, Tischbein, Vollenhoven, Forster, Kriechbaumer, Tasch- enberg, F. Smith, 0. G. Thomson, and Kondani. The last-men tioned author has published (in the Bulletin of the Italian Ento mological Society, 1871-78) a valuable list of parasitic insects and the species to which they are attached. (E. C. R.) ICHTHYOLOGY ICHTHYOLOGY 1 is that branch of zoology which treats of the internal and external structure of fishes, their mode of life, and their distribution in space and time. According to the views generally adopted at present, all those Vertebrate animals are referred to the class of Fishes which combine the following characteristics : they live in water, and by means of gills or branchiae breathe air dissolved in water ; the heart consists of a single ventricle and single atrium ; the limbs, if present, are modified into fins, supplemented by unpaired median fins ; and the skin is either naked, or covered with scales or with osseous plates or bucklers. . With few exceptions fishes are ovipar ous. There are, however, as we shall see hereafter, not a few members of this class which show a modification of one or more of these characteristics, and which, neverthe less, ca-nnot be separated from it. The distinction between the class of Fishes and that of Batrachians is very slight indeed. HISTORY AND LITERATURE. The commencement of the history of ichthyology coin- Aristotle, cides with that of zoology generally. Aristotle (384-322 B.C.) had a perfect knowledge of the general structure of fishes, which he clearly discriminates both from the aquatic animals with lungs and mammge, i.e.. Cetaceans, and from the various groups of aquatic invertebrates. According to him, " the special characteristics of the true fishes consist in the branchiae and fins, the majority having four fins, but those of an elongate form, as the eels, having two only. Some, as the Murcena, lack the fins altogether. The rays swim with their whole body, which is spread out. The branchiae are sometimes furnished with an operculum, some times they are without one, as in the cartilaginous fishes. . . . No fish has hairs or feathers ; most are covered with scales, but some have only a rough or a smooth skin. The tongue is hard, often toothed, and sometimes so much adherent that it seems to be wanting. The eyes have no lids, nor are any ears or nostrils visible, for what takes the place of nostrils is a blind cavity; nevertheless they have the senses of tasting, smelling, and hearing. All have blood. All scaly fishes are oviparous, but the cartilaginous fishes (with the exception of the sea-devil, which Aristotle places along with them) are viviparous. All have a heart, liver, and gall-bladder; but kidneys and urinary bladder are 1 From ix&vs, fish, and oyos, doctrine or treatise. absent. They vary much in the structure of their intes tines: for, whilst the mullet has a fleshy stomach like a bird, others have no stomachic dilatation. Pyloric caeca are close to the stomach, and vary in number ; there are even some, like the majority of the cartilaginous fishes, which have none whatever. Two bodies are situated along the spine, which have the function of testicles ; they open to wards the vent, and are much enlarged in the spawning season. The scales become harder with age. Not being provided with lungs, fishes have no voice, but several can emit grunting sounds. They sleep like other animals. In most cases the females exceed the males in size ; and in the rays and sharks the male is distinguished by an appendage on each side of the vent." Aristotle s information on the habits of fishes, their migrations, mode and time of propagation, and economic uses, is, so far as it has been tested, surprisingly correct. Unfortunately, we too often lack the means of recognizing the species of which he gives a description. His ideas of specific distinction were as vague as those of the fishermen whose nomenclature he adopted ; it never occurred to him that vernacular names are subject to change, or may be entirely lost in course of time, and the difficulty of identify ing his species is further increased by the circumstance that sometimes several popular names are applied by him to the same fish, or different stages of growth are designated by distinct names. The number of fishes known to Aristotle seems to have been about one hundred and fifteen, all of which are inhabitants of the ^Egean Sea. That one man should have discovered so many truths, and laid so sure a basis for future progress in zoology, is less surprising than the fact that for about eighteen centuries a science which seemed to offer particular attractions to men gifted with power of observation was no farther ad vanced. Yet such is the case. Aristotle s disciples, as well as his successors, remained satisfied to be his copiers or commentators, and to collect fabulous stories or vague notions. With very few exceptions (such as Ausonius, who wrote a small poem, in which he describes from his own observations the fishes of the Moselle) authors entirely ab stained from original research; and it was not until about the middle of the 16th century that ichthyology made a new step in advance by the appearance of Belon, Rondelet, and Salviani, who almost simultaneously published their great works, by which the idea of species was established
definitely and for all time.
