146 



COELENTERATA. 



-col 



tentacle is the single marginal tentacle of the medusoid which has 

 shifted on to the base of the manubrium. In some forms the gono- 

 phores become sexually mature while still attached to the stem, but 

 in the greater number the cormidia are detached before maturity 

 and become free-swimming. Such free-swimming groups are called 

 Eudoxia (Fig. 120), and are distinguished as monogastric forms 

 (there being only one mouth and stomach) from the polygastric 

 colonies from which they arise, and when found free are classified 



separately from the 

 polygastric forms, just 

 as the medusae of the 

 Anthomedusae are classi- 

 fied separately from the 

 polyp colonies. The 

 nutritive canals of all 

 the parts of a cormidium 

 unite in the bract (Fig. 

 120), from which point 

 a bracteal canal passes 

 to join the canal of the 



I stem. The phyllocyst 



I (Fig. 120), which corre- 

 sponds to the somatocyst 

 (Fig. 122), arises from 

 the same point. The 

 tentacle is tubular and 

 is beset with a series of 

 lateral tentilla, also tubu- 

 lar. Each tentillum is 

 composed of three parts 

 (1) a thin pedicle or 

 proximal part, (2) a 



dilated middle part the cnidosac, and (3) a slender terminal filament. 

 The swelling of the cnidosac is due to a rich development of nemato- 

 cysts of various kinds, forming the battery. 



The gonophore has a 4-radiate canal system and a velum, but is 

 without tentacles or mouth (Fig. 120). The sexual cells originate 

 in the ectoderm of its manubrium. It forms the swimming organ 

 of the cormidium. In some forms it becomes detached, and 

 then a secondary gonophore is formed. In some species (of Alyla) 

 a cluster of small gonophores is developed in a single cormidium, 



FIG. 121. Sphaeronectes gracilis (from Chun), seen from 

 the side, ny hydroecium : c.ol somatocyst ; c.v ventral 

 radial canal, c.d dorsal radial canal, c.c circular canal 

 of nectocalyx ; tr coenosome with connidia. 



