70 



HYDROZOA 



vertical axis, the indefiaite number (often also position) of 

 its tentacles, and its frequent formation of a colony of large 

 by lateral budding. By lateral budding (not by 



size 



?ia. 32.^Diagram showing possible modiflcations of persons of a gyinnoblastic 

 Sydromedvsa. a, hydrocaulus (stem); 6, hydrorbiza (root); c, entenc cavity; 

 d, endoderm; e, ectoderm; /,' perisarc (horny case); gr, hydvanth (hydriform 

 peraon) expanded ; ^, hydranth (hydriform person) contracted; h, hypostome, 

 bearing mouth at its extremity; *, succifonn gonophor (sporosac) springing 

 from the hydrocaulus; At*, sporosac spiinging from m, a modified hydriform 

 person (blastostyle) : the genitalia are seen surrounding the spadix or manu- 

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



metamerio 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 ffydromedusa. Letters a to A same as in fig. 32. i, the horny cup or 

 hydrotheca of the hydi'iform persons; I, medusiform person springing ftom m, 

 a modified hydriform person (blastostyle); n, the horny case or gonangiam 

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

 to the name Calyptdblastea. (.\fter 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 DUcophwos crypto- 

 carpce of Eschscholtz, the Craspedota of Gegenbaur (1854), and the 

 Hydromeduaida 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 



Pig. 34. 



Fig. 35. 



Fig. 84. — ^Diagram of Corymorpha. A, a hydriform person giving rise to 

 medusifoim persons by budding from the margin of the disc; B, free swim- 

 ming medusa (Steensfrupia of Forbes) detached from the same, with manu- 

 brialgenitalia (Anthomedusce) and only one tentacle. (After Allman.) 



Fig. 35. — Diagram of Tubulwia indivisa. A single hydriform person a bearing a 

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

 Allman.) 



Sydroida (together with Lucemaria), 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 

 Mydromedusce 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 medusas of Esehscholtz and the 



Fio. 36. — Colony of Bougainvillea fruticosa, natural size, attached to the 

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



hydroids related to them. The term Hydromedv^ce is used unwisely 

 by Claus {Cfrundziige 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 medusifoim 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 seta of persons under one 

 system. 



Order 1. GymnohlasteorAnthomedtisoe. — These are jffycfro- 

 medmae 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 



