HYDROZOA 



71 



persons may secrete a horny tubular protective case 

 (perisarc), hut 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. Portion of colony of BougainriUea (Eiidendrhtu>)frtttico!;a (Anttiomeduscp- 

 catyptoblaslea) more magnified. (From Lubbnck, alter Aliman.) 



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). 



This is a very well defined group, since tlie GymnoWastea of 

 Allman, liased on the eh.-iraetcrs of the liydrifnrm ]iursous also 

 known as Tiiliiilm-in- ;\m\ iti/mnotoka correspond exactly with the 

 Antliniiii'iliimr of Ilaeekid'.s new system, llijdra is included here, 

 though placed in a separate order liy Aliman. Some of the leading 

 forms of hydriform and inedusiform 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 

 medusse, the latter sessile .sporosacs. The (Jccanitlcc of Gegenliaur 

 (excluding the Williadit, which Haeekel assigns to the next group) 

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



Fig. 41. 



Fig. 42. 



FIG. 41. Hydriform person of Simcorime, witlimedusifnmi persons budding from 

 it. and shoun in various stages of development, a, 6, c, d, e. (From Gegenbaur, 

 after Desor.) 



FIG. 42. Hiidra riridis. ot, ovary; te, testis. 



Order 2. Calyptoblastea-Leptomedmce. These are Hydro- 

 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. 38. 



Fig. 39. 



Fig. 40. 



FIG. 3S. Diagram of Clara, showing a hydriform person surrounded by a 

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



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

 hydriform person ; 6, modified hydriform person,' or blastnstyle bearing r 

 degi-nerate medusiform persons or sporosacs; d, mndifled hydriform person 

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



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

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

 stylc); c, degenerate medusiform persons (sporosacs).' (After Aliman.) 



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. 



Fig. 43. Fig. 44. 



FIG. 43. Diagram of a colony of f'ampiinularia. showing four forms of per- 

 sons. A, portion of a fixed colony ; a. hydrifonn person ; fc, bud-bearing 

 hydrifoi-m person (blastostyle) ; B, flee -swimming colony, being a sexless 

 medusiform person (blastocheme of Aliman), with modified medusiform persons 

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



FIG. 44. Medusiform person (Li::ia), one of the Antliomeditsts, detached from a 

 hydroid colony of the fnmily iWi'WnW.r. ( icelli are seen at the base of the 

 tentacles, and two medusiform buds on the sides of the iu:inubrium. (After 

 Aliman.) 



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 



