Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/576

560 560 HYDROZOA vertical axis, the indefinite number (often also position) of its tentacles, and its frequent formation of a colony of large size by lateral budding. By lateral budding (not by Fio. 32. Diagram showing possible modifications of persons of a gymnoblastic Hydromedusa. a, hydrocaulus (stem); 6, hydrorhiza (root); c, enteric cavity; d, endoderm ; e, ectoderm ; /, perisarc (horny case) ; g, hydranth (hydrif orm person) expanded; g 1, hydranth (hydriform person) contracted; h, hypostome, bearing mouth at its extremity; k, sacciform gouophor (sporosac) springing from the hydrocaulus; k , sporosac springing from m, a modified hydriform person (blastostyle): the genitalia are seen surrounding the spadix or manu- brium; I, medusif orm person or medusa; m, blastostyle. (After Allman.) metameric fission) medusiform persons which alone develop sexual glands are produced on the hydriform colonies; 7, FIG. 33. Diagram showing possible modifications of the persons of a Calypto- blastic Hydromedusa. Letters a to h same as in fig. 32. i, the horny cup or hydrotheca of the hydriform persons; I, medusiform person springing from m, a modified hydriform person (blastostyle) ; n, the horny case or gonangium enclosing the blastostyle imd its buds. This and the hydrotheca i give origin to the name Calyptoblastea. (After Allman.) these may separate from the colony, or may be retained in a more or less degenerate form adherent to it, as generative buds or warts. The medusiform persons of this group are the DiscopJiorce crypto* carpce of Eschscholtz, the Craspedota of Gegenbaur (1854), and the Hydromedusida of Kolliker (1853) the last two authors at that time separating the hydriform persons as Hydroidea. Louis Agassiz (1860) includes both sets of persons under the term Fig. 35. FIG. 34. Diagram of Corymorpha. A, a hydriform person giving rise to medusiform persons by budding from the margin of the disc; B, free swim ming medusa (Steenstnipia of Forbes) detached from the same, with manu- brial genitalia (Anthomedusce) and only one tentacle. (After Allman.) FIG. 35. Diagram of Tubulariaindivisa. A single hydriform person a bearing a stalk carrying numerous degenerate medusiform persons or sporosacs 6. (After Allman.) Hydroida (together with Lucernaria), which also is the term adopted by Allman in his beautiful monograph (1871-74). J.V. Cams, amend ing the limitations given by Carl Vogt, was the first to use the term Hydromedusce in the sense here adopted (Handbuch der Zoologie, 1863), and it is now employed in the same sense by Gegenbaur (Elements of Comparative Anatomy, London, 1878), namely, to em brace both the cryptocarpous meduste of Eschscholtz and the FIG. 3G. Colony of BougainriUea fruticosa, natural size, attached to the underside of a piece of floating timber. (After Allman.) hydroids related to them. The term Hydromedusce is used unwisely by Glaus (Grundziige d. Z.) for the whole group of Hydrozoa. _ It has been the practice of some authors to give a double classification of the group one based on the characters of the medusiform per sons, the other on that of the hydriform persons. In the present article a double name will in some cases be assigned to a group but the attempt is made to bring both sets of persons under one system. Order 1. Gymnoblastea-Anthomedusce. These are Hydro medusce which all, as far as is known, pass through a hydriform phase, but in which the medusiform persons may either reach full development or exhibit the extremest degeneration (Hydra). The ectoderm of the hydriform