122 OUTLINES OF EVOLUTIONARY BIOLOGY 



separates from the parent colony, but remains attached to it as a 

 bud, though still showing clear evidence, in its bell-like shape and 

 in the presence of the manubrium and of radial and circular 

 canals, of its medusoid nature. It is in fact merely a degenerate 



ten. 



FlG. 61. A single Hydranth of Tubularia, with medusoid Individuals 

 (Gonophores) budded out between the two Circles of Tentacles ; highly 

 magnified. (After Allman.) 



act., actinula larva enclosed in gonophore ; act. ', actinula larva escaping ; ent., enteron 

 or digestive cavity ; gon., gonophore ; ?., mouth ; per., perisarc ; ten., tentacles. 



medusa or gonophore (Fig. 61, gon.). It still retains its sexual 

 function, producing either ova or spermatozoa, and in this case 

 the fertilized ova actually develop into young hydroids or 

 " actinula larvae " (Fig. 61, act., act.') before escaping from the 

 parent gonophore. We have here a telescoping of the successive 

 generations quite comparable to what we find in a flowering 



