HYDRO ZOA 



71 



persons may secrete a horny tubular protective case 

 (perisarc), but this does not form cups for the reception of 

 the tentacular crown nor cases enclosing groups of medusi- 

 form buds (gonangia). The fully-developed medusiform 



Fig. 37. — Vortionof co\ojiy of BougainviUea(Endendnum) fruficosa^Anthomedusce- 

 calyptoblastea) more magnified. (From Lubbock, after Allman.) 



persons never possess otooysts nor tentaculocysts, but always 

 ocelli at the base of the tentacles. The latter are usually 

 four or six, corresponding to the same number of simple 

 radial enteric canals, but may be more numerous or reduced 

 to one or to two ; rarely they are branched {Cladonema), 



Fio. 88.— Diagram of Clava, showing a liydriform person sun-ounded by a 

 verticil of degenerate medusiform persons (sporosacs). (After Allman.) 



Fig. 39. — Diagram of a colony of Hydractima,i showing four fouai of persons, a, 

 liydriform person; *, modified hydriform person, or blastostyle, bearing c, 

 degenerate medusiform persons or sporosacs; d, modified hydriform person 

 situated at the margin of the colony (dactylozooid). (After Aliman.) 



Fig. 40.— Diagram of a colony of Dicoryne^ showing three forms of persons, a, 

 normal hydriform person ; 6, modified bad-bearing hydriform person (blasto- 

 style) ; c, degenerate medusiform persons (sporosacs). (After Alhnan.) 



The sexual glands are placed in the wall of the manubrium, 

 either equally distributed all round it or in four separate 

 perradial groups, which are often divided into eight ad- 

 radial groups by the perradial longitudinal muscles. , 



This is a very well defined group, since the Oymnoblastea of 

 Allman, based on the characters of the hydriform persons — also 

 known as Tuhularim and Gymnotoka — correspond exactly with the 

 Anthomeduste of Haeokel's new system. Hydra is included here, 

 though placed in a separate order by Allman. Some of the leading 

 forms of hydriform and medusiform persons are given in the cuts 

 (figs. 34 to 42). The greatest range in the amount of degenera- 

 tion of the medusiform persons is seen even in genera of the same 

 family — e.g., Turris and Clava — the former producing free 

 medusie, the latter sessile sporosacs. The Oceanidce of Gegenhaur 

 (excluding the WilUadoe, which Haeckel assigns to the next group) 

 correspond on the whole to the medusa-forms of this order. 



Pig. 41. Fig. 42. 



Fig. 41. — Hydriform person of Syncoryne, witli medusiform persons budding from 



it. and shown in various stages of development, a, &, c, tf, e. (From Gegenbaur, 



after Desor.) 

 Fig. 42, — Hydra viridis, o«, ovaiy; te, testis. 



Order 2. Calyptoblastea-Leptomedusce. — These are Hydro- 

 meduscB of which the hydriform phase is known in a 

 large number of cases, whilst of others only the medusa- 

 forms are known ; none are hnown to develop directly from 

 the egg to the medusa-form. As in the preceding group, 

 the medusiform persons may reach full development or 



Fig. 43. Fig. 44. 



Fig. 43. —Diagram of a colony of Campanularia, showing four forms of per- 

 sons. A, portion of a fixed colony; a. hydriform person ; &, bud-bearing 

 hydriform person (blastostyle) ; B, free - swimming coltiny, being a sexless 

 medusiform person (blastoeheme of Allman), with modified medusiform persons 

 budding from its radiating canals, as sporosacs. (After Allman.) 



Fig. 44. — Medusiform person [Lizzia\ one of the AntJtomedmce, detached from a 

 hydroid colony of the family Endendridos. Ocelli are seen at the base of the 

 tentacles, and two medusiform buds on the sides of the manubrium. (After 

 Allman.) 



exhibit themselves as degenerate sexual sacs on the hydri- 

 form colonies. The ectoderm of the hydra-forms always 

 secretes a perisarc which forms a cup-like protection (hydro- 

 theca) to the tentacle-crown, and which also encloses the 

 group of medusa-buds in peculiar horny cases (gonangia). 

 The fully-developed medusiform persons (fig. 47) either 



