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 Jcochii. The embryo 

 gives rise to a form with a single 

 nectocalyx which is like a Mono r pliyes, 

 and this by the budding of a second N 

 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 Fig. 142. Free-swinmiiug Mrsaea 

 is formed at the base of each one 

 of them, and the group of zooids is 

 detached as an independent colony, 

 formerly known as Eudoxia escJischol- 

 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 



group of Doramasia jjicta. 

 B, B, batteries of nematocysts 

 borne by the tentilla ; D, 

 dactylozooid ; G, gastrozooid ; 

 H, hydrophyllium ; A", necto- 

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

 minal filament of a battery ; 

 t , t, tentilla. The gonozooid 

 is hidden by the gastrozooid. 

 x 10. (After Chun.) 



