THE HYDROMEDUSAE 



43 





Fig. 48a. 



Fio. 48. 



4.S.— Dia<;rain of the structure of Velella, showiiiiL,' llie central and peripheral thirds of 

 a half-section of the colony, the middle third being omitted. 'I he ectwlenn is indicated by 

 close hatchin',', the endodenii by li^ht hatching, the mesogloea by thick black lines, the homy 

 skeleton of the pneumatophore and sail by dotting. /;/,, blaslostyle ; C, centnidenia ; D, dacty- 

 lozooid ; EC, edge of colony, prolongi'il V)eyond the pneinnatophore ; ii, cavity of the large 

 central gastrozooid ; ,U, mednsoids attached to blastostyles ; i'A', i)rimary central chamber, ami 

 i'iV, a concentric chamber of the i)nenmatophore, the fonner showing the opening into the 

 Hecond chamber, the latter showing an ojiening to the exterior, and a " trachea " ; .s', .sail. 



48f(. —i'oryn'ta from the aboral aspect, showing the jineuinatophore, and expanded dactylo- 

 zooids. (After Agassiz.) 



