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* HYATT. 357 HYBRIDITY. throughout the Civil War, rising to the rank of captain. He afterwards renewed his studies, be- coming curator of the Es.sex Institute in 1867. He was the principal founder of the American Society of Naturalists; organized a seaside lab- oratory at Amusquam, Mass. ; took part in the organization of the Marine Biological Laboratory at Wood's Holl. JIass.; and assisted in the founding of the Peabody Academy of Sci- ences, and became its curator in 1809. He was also one of the founders of the American Xafuralist. In 1870 he became custodian, and in 1881 curator, of the Boston Society of Natural History, and in 1881 was appointed professor of zoology and paleontology at the Massachusetts Institute of Technology and at Boston University. He was elected a member of the National Academy of Sciences in 1875; was a correspond- ing member of the Geological Society of London; and in 1898 received the degree of LL.D. from Brown University, and was a vice-president of the American Academy of Arts and Sciences, Boston. His work as a paleontologist was mas- terly; besides making many innovations in the classification of the nautiloids and ammonites (q.v.), the final results form the most valuable contribution to the philosophy of biologj'. He was the founder of the new school of invertebrate paleontologj'. In systematic zoology he jvill be remembered for being next to the first one to refer the sponges to a distinct phylum. He also proposed many new genera, families, and numer- ous suborders of fossil cephalopods. He dis- covered the law of acceleration in the evolution of Cephalopoda, and the mechanical causes of their evolution; of his work on the fossil pond- snails of Steinheim and the origin of their vari- ous forms. Sir R. Owen wrote that it was "a model of the way and aim in and by which such researches should be conducted." Hyatt wrote, besides many shorter articles : Ob- servations on Freshimler Polyzoa (1866); Re- vision of 'North American Porifera (1875-77); ''The Genesis of the Tertiary Species of Planorbis at Steinheim," in Memoirs of the Boston Hociety of Natural History (1880); Genera of Fossil Cephalopods (1883) ; Larval Theory of the Ori- gin of Cellular Tissue (1884); The Genesis of the Arietidw (1889). He has edited Guides to Science Teaching, and revised the part of the Zittel-Eastman Text-book of Paleontology on Nautiloids and Ammonoids. These works make him prominent among the new school of Ameri- can zoiilogists. led by Cope and Packard, which called itself 'Neo-Lamarckian.' Professor Hyatt died at Cambridge in 1902. HYATT, .loiiN Wesley (]8:i7— ) . An Ameri- can inventor, born at Starkey, N. Y. His educa- tion was very meagre, and while yet in his teens Hyatt started upon his career as ail inventor. His first important invention (186.5) was that of a composition liilliaid-liall which. by reason of the scarcity of ivory, became very popular. Four years later. l>y liis discovery of a means for dis- solving pyroxylin under ju-essure, he laid the foundations for the present immense celluloid industry. Undoubtedly Hyatt's greatest contri- bution to science, however, was the scheme he devised in ISSl for the purifying of large bodies of water. The success of his method lias been attested by the general use made of it both in the United States and abroad. HY^BLA (Lat., from Gk.°T^,). The name of two Ujwns in Sicily. Hybla Major was sit- uated on the seacoast, not far from Syracuse, and Hybla Minor at the foot of Etna" Both were originally cities of the native inhabitants, and were afterwards Hellenized. From one of these came the Hyblaean honey, rendered so fa- mous by the poets. HYBODUS, hib'A-dus (Neo-Lat., from Gk. i'liot, hybus, hump + 6(io6s, odous, tooth). An e.xtinct genus of cestraciont sharks found fo.ssil in the Triassic and .Jurassic rocks. Finely pre- served skeletons of this shark have been found in tile Liassic deposits of England. These fish had blunt heads, jaws armed with nine to ten rows of sharp, conical teeth, fins armed with long, sharp, anterior spines, and the skin was covered with shagreen, consisting of small pointed plates. Two sharp curved spines on each side of the head behind the eyes are present on the males only, and perhaps served as offen- sive organs. The species varied from three to six feet in length. See Sh.^rk. HYBRID (from Lat. hybrida, hibrida, ibrida, hybrid), in plants. The progeny of parents which belong to diflerent species or races. See Hy- BRIDITY. HYBRIDITY. The phenomenon of the sex- ual crossing of two individuals belonging to dis- tinct species. A hybrid is the product of this crossing, and is contrasted with a mongrel, or the product of individuals belonging to distinct races or varieties of the same species. The importance of hybridity is threefold : { 1 ) A Test of Species. — Hybridity has been used by Cuvier and others as a test of species, as contrasted with varieties. It has been assert ed that hybrids are sterile, whereas mongrels are fertile. So long as infertility of descendants is used as a criterion of species, this tenet is un- assailable; the difficulty arises from the fact that the strict application of the criterion leads us to deny specific distinctions to animals that are commonly regarded as such — e.g. the dog and wolf, dog and jackal, the hare and rabbit, vari- ous species of Bovidse or oxen, sheep and goat, and, among plants, various forms of Rhododen- dron, Gladiolus. Dianthus, Nicotiana, etc. Focke says concerning plants: "Many hybrids, especial- ly those between unlike lines of descent, are in- fertile, most show a diminished fertility, some a nearlji normal fertility." It may be concluded, therefore, that the Cuvierian definition of spe- cies will not hold. While fertile hybrids are thus not common, the capacity for hybridization in the first generation is widespread. The question arises, Why are hybrids so often sterile ? Various hypotheses have been proposed, but none can be said to be proved. Darwin's hypothesis is thus summarized : "The sterility of first crosses and of their hybrid progeny has not been acquired through natural selection. In the case of first crosses it seems to depend on several circumstances ; in some instances on the early death of the embryo. In the case of hy- brids, it apparently depends on their whole or- ganization having been disturbed by being com- pounded from two distinct forms, the sterility being closely allied to that which so frequently affects pure species when exposed to new and un- natural conditions of life. He who will explain these latter cases will be able to explain the