SIPHONOPHORA 



displaced from their original position. The manubrium has come to 

 lie outside the medusa bell as the gastrozooid, and the gonads and 

 tentacles have also become separated. In the early stage of development 



Fig. 122. Examples of Siphonophora. A, Velella. Altered from Haeckel. 

 Vertical section, showing the cavity of the pneumatophore (stippled) and 

 produced into branching gas tubes, the tracheae {tra.), and a network of 

 endodermal tubes (black), which arise from the cavity of the gastrozooid 

 and gonozooids (black); med. medusa buds. Other letters as in Fig. 121. 

 B, Physalia showing the "drift net" arrangement of the tentacles of the 

 dactylozooids. 



of a siphonophore colony shown in Fig. 121 B, there are two necto- 

 calyces and two groups (cormidia) of the displaced organs which 



