IV 



COELENTERATA 



emb 



B 



creeping stolons which give rise at intervals to other upright shoots. 

 Its lower part secretes a horny shell, the perisarc. 



The adult colony, 

 however, is still unripe 

 sexually ; full sexual ma- 

 turity is only reached by 

 thegonophores produced 

 subsequently, and thus 

 we have an alternation 

 of asexual and sexual 

 generations. 



The development of 

 these gonophores in 

 the case of Tubularia 

 (as well as in the case of 

 many other genera) has 

 been worked out by 

 Gotte (1907) ; we follow 

 his account in what 

 follows. From just above 

 the region of the aboral 

 tentacles, finger-like 

 stolons grow out, and on 



A, gonophore with discoid embryo ; opening of umbrella-cavity 

 just formed ; radial canals clear. B, gonophore with actinula 

 larva just escaping ; radial canals have disappeared. Act, actinula ; 

 emb, embryo; r.c, radial canal; sp, manubrium or spadix ; ?i, 

 opening of umbrella-cavity. 



at. 



Act 



FIG. 32. Two gonophores of Tubularia indivisa with 

 developing embryos inside. (After Allman.) 



these, lateral protrusions 

 arise, which are the 

 medusa -buds. At the 

 tip of such a bud, the 



FIG. 33. Stages in development of Actinula larva of Tubularia indivisa. (After Allman.) 

 A, creeping larva. B, first fixed form, ab.t, aboral tentacles ; o.t, oral tentacles ; y/cc, perisarc ; 



si, stolon. 



ectoderm thickens to form a mass of cells, and in this mass a cavity 

 develops, the future umbrella-cavity. 



