SIPHONOPHORA 



303 



larva (i.e. the side opposite to the pneumatophore), a definite 

 octoradial symmetry is shown, there being for some time eight 

 dactylozooids and eight definite folds in the wall of the 

 pneumatophore. This octoradial symmetry, however, is soon 

 lost as the number of folds in the pneumatophore and the 

 number of tentacles increase. 



It is probable that in the Siphonophora, as in many other 

 Coelenterata, the production of sexual cells by an individual is 

 no sign that its- life -history is com- 

 pleted. There may possibly be two or 

 more phases of life in which sexual 

 maturity is reached. 



An example of a complicated life- 

 history is found in the Calycophoran 

 species Muggiaea kochii. The embryo 

 gives rise to a form with a single 

 nectocalyx which is like a Monophges, 

 and this by the budding of a second w- 

 nectocalyx produces a form that has a 

 remarkable resemblance to a Diphyes, 

 but the primary nectocalyx degenerates 

 and is cast off, while the secondary one 

 assumes the characters of the single 

 Muggiaea nectocalyx. The stolon of 

 the Muggiaea produces a series of 

 cormidia, and as the sexual cells of the 

 cormidia develop, a special nectocalyx ^-^■^^rS:^^!'';^:: 



is formed at the base of each one s, B, batteries of nematocysts 



of them, and the group of zooids is 



detached as an independent colony, 



formerly known as Uudoxia eschscJiol- 



tzii. In a similar manner the cormidia 



of Doramasia picta give rise to the 



sexual free - swimming monogastric 



forms, known by the name Ersaea picta (Fig. 142). In these 



cases it seems possible that the production of ripe sexual cells is 



confined to the Eudoxia and Ersaea stages respectively, but it is 



probable that in other species the cormidia do not break off from 



the stolon, or may escape only from the older colonies. 



The Siphonophora are essentially free - swimming pelagic 



borne by the tentilla ; D, 

 dactylozooid ; 6, gastrozooid ; 

 H, hydrophyllhim ; N, necto- 

 calyx ; 0, oleocyst ; /, t, ter- 

 minal filament of a battery ; 

 t.i, tentilla. The gonozooid 

 is hidden by the gastrozooid. 

 X 10. (After Chun.) 



