XXI II 



tNDIVIDUATION 



253 



logical and physiological differentiation are thus carried 

 much further than in such a form as Bougainvillea. 



FIG. 59. A. Porpita pacific a (nat. size), from beneath, showing disc- 

 like stem surrounded by tentacles (/), a single functional hydranth (hy], 

 and numerous mouthless hydranths (hy'). 



B, vertical section of P. mcditen-anca, showing the relative positions 

 of the functional (hy} and mouthless (Iiy'} hydranths, the tentacles, 

 and the chambered shell (s/i). (A after Duperrey ; B from Huxley after 

 Kolliker.) 



Porpita is another free-swimming Hydroid, presenting at 

 first sight no resemblance whatever to Diphyes. It has much 

 the appearance of a flattened medusa (Fig. 59), consisting 

 of a circular disc, slightly convex above and concave below, 



