70 



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 



?IG. 32. Diagram showing possible modifications of persons of a gymnoblastic 

 ffydromedusa. a, hydrocaulus (stem); 6, hydrorhiza (root); c, enteric cavity; 

 d, endoderm; c, ectoderm; f, perisarc (horny case); (/, hydranrh (hydriform 

 person) expanded; g', hydra'nth (hydriform person) contracted; h, hypostome, 

 bearing mouth at its extremity; A-, sacciform gonophor (sporosac) springing 

 from the hydrocaulus; k', sporosac springing from m, a modified hydriform 

 person (blas'tostyle): the genitalia are seen surrounding the spadix or manu- 

 brium; /, medusiform person or medusa; m, blastostyle. (Alter Allman.) 



metameric fission) medusiform persons which alone develop 

 sexual glands are produced on the hydriform colonies; 



FIG. 33. Diagram showing possible modifications of the persons of a Calypto- 

 blastic HydromeduRa. Letters a to A same as in fig. 32. I, the horny cup or 

 hydrothe.ca of the hydriform persons; /. medusiform person springing from in, 

 a modified hydriform person (blastostyle); 71, the horny case or gonangittm 

 enclosing the blastostyle and its buds. This and the hydrotheca t give origin 

 to the name Calyptoblastea. (After Allnian.) 



these may separate from the colony, or may be retained in 

 a more or less degenerate form adherent to it, as generative 

 bucls or warts. 



The medusiform persons of this group are the DismphariK crypto- 

 carpcc of Eschscholtz, the Craspcdota of Gegenbaur (1854), and the 

 Hydromedusida of Kolliker (1853) the last two authors at that 

 time separating the hydriform persons as Hydroidca. Louis 

 Agassiz (1860) includes both sets of persons under the term 



Fig. 34. 



Fig. 35. 



PIG. 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 (Steenstrupia of Forbes) detached from the same, with manu- 

 brial genitalia (Anthomedustp) and only one tentacle. (After Allmun.) 



FIG. 35. Diagram of Tubutaria irtilivisa. A single hydriform person a bearing a 

 stalk carrying numerous degenerate medusiform persons or sporosacs 6. (After 

 Allnian.) 



Hijdroida (together with Lucernaria), which also is the term adopted 

 byAllnian in his beautiful monograph) 1871-74). J.V. Cams, amend- 

 ing the limitations given by Carl Vogt, was the first to use the term 

 Hydromcdusce 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 medusae of Eschscholtz and the 



FIG. 36. Colony of Bougainvillea fivtieosa, natural size, attached to the 

 underside of a piece of floating timber. (After Allman.) 



hydroids related to them. The term Hydromcdusos is used unwisely 

 by Claus (Gnindziigc 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. GymnoUastea-Anthomedusof. These are Hydro- 

 medusa?, 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 



