HYDROZOA 



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 rnedusiform 



FIG. 37. Portion of colony of BaugainrUlta (Endedrivm)fr*tiaua {A nthomeduur- 

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



persons never possess otocysts 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). 



Fig. 38. 



Fig. 39. 



Fig. 40. 



FIG. 38. Diagram of Clara, showing a hydriform person surronnded by a 

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



FIG. 39. Diagram of a colony of Hydraftinia,' showing four forms of persons, a, 

 hydfiform person; 6, modified hydriform person, or blastustyle, bearing c, 

 degenerate mednsiform persons or sporosacs; d, modified hydriform person 

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



FIG. 40. Diagram of a colony of Diearne, showing three forms of persons a, 

 normal hydriform person : 6, modified bud-bearing hydriform person (blasto- 

 style); f, degenerate mednsiform persons (sporosacs).' (After Allman.) 



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

 either equaUy 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 Gymnoblastea of 

 Allman, based on the characters of the hydrifonn persons also 

 known as Tubnlaruz and Gymnatokor correspond exactly with the 

 AnUtomeduste of Haeckel's new system. Hydra is included here, 

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

 forms of hydriform and medusifonn persons are given in the cuts 

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

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

 family e.g., Turns and data the former producing free 

 medusae, the latter sesrile sporosacs. The Occanidte of Gegenbaur 

 (excluding the Williada:, which Haeckel assigns to the next group) 

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



Fig. 41. Fig. 42. 



FIG. 41. Hydrifonn person of SfKorfttt, with medosif orm persons budding from 



it. and shown in various stages of development, o, b, c, d, e. (From Gegenbaur, 



after Desor.) 

 FIG. 42. Hvdra riridis. or, ovary; te. testis. 



Order 2. Calyptoblastea-Leptomedusa;. These are Hydro- 

 medusae of which the hydriform phase is known in a 

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

 forms are known ; none are known 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 Campantilaria. showing four forms of per- 

 sons. A, portion of a fixed colony; a. hydriform person; 6, bud-bearing 

 hydriform person (blastostyle) ; H, free - swimming colony, being a sexless 

 mednsiform person (blastocheme of Allman). with modified medusiform persons 

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



FIG. 44. Medusiform person (Liiria). one of the Anthomedanx, detached from a 

 hydroid colony of the family EndtndH&r. Ocelli are seen at the base of the 

 tentacles, and two mednsiform 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-deveJoped medusifonn persons (fig. 47) either 



