58 



HYDROZOA 





The youngest examples of the group seen as yet 



Fig. ii. 



Development of Physalia : 



young Physalia, with a sing 



le 



polypite and tentacle ; J, the same, more advanced ; c, adult P^" 



4 a « _* f 



safoa; d, a tentacle, with its basal sac; — a, pneumatophore ; «'» 

 pneumatocyst ; tt, polypite ; t, tentacle, (a and b are magnified ; 

 c is reduced ; d is about the natural size. ) 



exhibit a well-defined pneumatophore, with a single 

 polypite and tentacle {fig. u, a). 





