58 HYDROZOA. 



The youngest examples of the group seen as yet, 



Fig. II. 



Deyelopment of Physalia: — a, young Fhysalia, with a single 

 polj-pite and tentacle ; b, the same, more advanced ; c, adult P%- 

 salia ; d, a tentacle, with its basal sac; — o, pneumatophore ; a', 

 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. ii, a). 



