146 



THE INVERTEBRATA 



Fig. 121. Development of the siphonophore colony. A, Diagram of the 

 possible combinations of individuals in a colon3\ The continuous gastro- 

 vascular system is shown in black, pn. pneumatophore ; nee. nectocalyx; 

 hyd. hydrophyllium ; gst. gastrozooid; dac. dactylozooid with its tentacle; 

 gnz. gonozooid; cor. cormidium; esc. coenosarc; ten. branched tentacle, 

 sometimes springing from the base of the gastrozooid. B, Early stage of colony 

 of Muggiaea, showing two generations of nectocalyces, nec.^, nec.'~ can.r. the 

 radial canals of the first nectocalyx. Other lettering as in A. nec.^ is lost 

 later and nee.- becomes the single permanent nectocalyx of the colony; pn. is 

 really an oleocyst and not a pneumatophore. C, Sarsia, an anthomedusan, 

 for comparison, showing budding of daughter medusae from the end of the 

 radial canals. 7tinb. manubrium; med. daughter medusae. A, altered from 

 Hertwig; B, after Chun; C, after Allman. 



