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 parthenogenetically, that is to say without the intervention of males, and by a process that has been compared to internal budding, large numbers of young resembling their parents in every particular except size, which themselves reproduce their kind in the same way. This process continues throughout the summer, generation after generation being produced until the number of descendants from a single individual of the spring-hatched brood may amount to very many thousands. In the autumn winged males appear, union between the sexes takes place and the females lay the fertilized eggs which are destined to carry the species through the cold months of winter. If, however, the food-plant is grown in a conservatory where protection against cold is afforded, the aphides may go on reproducing agamogenetically without cessation for many years together. Not the least interesting features connected with this strange life-history are the facts that the young may be born by the oviparous or viviparous methods and either gamogenetically or agamogenetically, and may develop into winged forms or remain wingless, and that the males only appear in any number at the close of the season. Although the factors which determine these phenomena are not clearly understood, it is believed that the appearance of the males is connected with the increasing cold of autumn and the growing scarcity of food, and that the birth of winged females is similarly associated with decrease in the quantity or vitiation of the quality of the nourishment imbibed. Sometimes the winged females migrate from the plant they were born on to start fresh colonies on others often of quite a different kind. Thus the apple blight (Aphis mali) after producing many generations of apterous females on its typical food-plant gives rise to winged forms which fly away and settle upon grass or corn-stalks.

Closely related to the typical aphides is Phylloxera vastatrix, the insect which causes enormous loss by attacking the leaves and roots of vines. Its life-history is somewhat similar to that of Aphis rosae summarized above. In the autumn a single fertile egg is laid by apterous females in a crevice of the bark of the vine where it is protected during the winter. From this egg in the spring emerges an apterous female who makes a gall in the new leaf and lays therein a large number of eggs. Some of the apterous young that are hatched from these form fresh galls and continue to multiply in the leaves, others descend to the root of the plant, becoming what are known as root-forms. These, like the parent form of spring, reproduce parthenogenetically, giving rise to generation after generation of egg-laying individuals. In the course of the summer, from some of these eggs are hatched females which acquire wings and lay eggs from which wingless males and females are born. From the union of the sexes comes the fertile egg from which the parent form of spring is hatched.

APHORISM (from the Gr. , to define), literally a distinction or a definition, a term used to describe a principle expressed tersely in a few telling words or any general truth conveyed in a short and pithy sentence, in such a way that when once heard it is unlikely to pass from the memory. The name was first used in the Aphorisms of Hippocrates, a long series of propositions concerning the symptoms and diagnosis of disease and the art of healing and medicine. The term came to be applied later to other sententious statements of physical science, and later still to statements of all kinds of principles. Care must be taken not to confound aphorisms with axioms. Aphorisms came into being as the result of experience, whereas axioms are self-evident truths, requiring no proof, and appertain to pure reason. Aphorisms have been especially used in dealing with subjects to which no methodical or scientific treatment was applied till late, such as art, agriculture, medicine, jurisprudence and politics. The Aphorisms of Hippocrates form far the most celebrated as well as the earliest collection of the kind, and it may be interesting to quote a few examples. “Old men support abstinence well: people of a ripe age less well: young folk badly, and children less well than all the rest, particularly those of them who are very lively.” “Those who are very fat by nature are more exposed to die suddenly than those who are thin.” “Those who eject foaming blood, eject it from the lung.” “When two illnesses arrive at the same time, the stronger silences the weaker.” The first aphorism, perhaps the best known of all, which serves as a kind of introduction to the book, runs as follows:—“Life is short, art is long, opportunity fugitive, experimenting dangerous, reasoning difficult: it is necessary not only to do oneself what is right, but also to be seconded by the patient, by those who attend him, by external circumstances.” Another famous collection of aphorisms is that of the school of Salerno in Latin verse, in which Joannes de Meditano, one of the most celebrated doctors of the school of medicine of Salerno, has summed up the precepts of this school. The book was dedicated to a king of England. It is a disputed point as to which king, some authorities dating the publication as at 1066, others assigning a later date. The dedication gives the following excellent advice:—

Another collection of aphorisms, also medical and also in Latin, is that of the Dutchman Hermann Boerhaave, published at Leiden in the year 1709; it gives a terse summary of the medical knowledge prevailing at the time, and is of great interest to the student of the history of medicine. APHRAATES (a Greek form of the Persian name Aphrahaṭ or Pharhadh), a Syriac writer belonging to the middle of the 4th century, who composed a series of twenty-three expositions or homilies on points of Christian doctrine and practice. The first ten were written in 337, the following twelve in 344, and the last in 345. The author was early known as ḥakkīmā phārsāyā (“the Persian sage”), was a subject of Sapor II., and was probably of heathen parentage and himself a convert from heathenism. He seems at some time in his life to have assumed the name of Jacob, and is so entitled in the colophon to a MS. of 512 which contains twelve of his homilies. Hence he was already by Gennadius of Marseilles (before 496) confused with Jacob, bishop of Nisibis; and the ancient Armenian version of nineteen of the homilies has been published under this latter name. But (1) Jacob of Nisibis, who attended the council of Nicaea, died in 338; and (2) our author, being a Persian subject, cannot have lived at Nisibis, which became Persian only by Jovian’s treaty of 363. That his name was Aphrahat or Pharhādh we learn from comparatively late writers—Bar Bahlul (10th century), Elias of Nisibis (11th), Bar-Hebraeus, and ʽAbhd-īshō’. George, bishop of the Arabs, writing in 714 to a friend who had sent him a series of questions about the “Persian sage,” confesses ignorance of his name, home and rank, but infers from his homilies that he was a monk, and of high esteem among the clergy. The fact that in 344 he was selected to draw up a circular letter from a council of bishops and other clergy to the churches of Seleucia and Ctesiphon and elsewhere—included in our collection as homily 14—is held by Dr W. Wright and others to prove that he was a bishop. According to a marginal note in a 14th-century MS. (B.M. Orient. 1017), he was “bishop of Mar Mattai,” a famous monastery near Mosul, but it is unlikely that this institution existed so early. The homilies of Aphraates are intended to form, as Professor Burkitt has shown, “a full and ordered exposition of the Christian faith.” The standpoint is that of the Syriac-speaking church, before it was touched by the Arian controversy. Beginning with faith as the foundation, the writer proceeds to build up the structure of doctrine and duty. The first ten homilies, which form one division completed in 337, are without polemical reference;