PLATE IV. 



Fid. 



1. HYDRACTINIA ECHINATA, p. 23, nat. size. 



2. A group of the same (female) , magnified. 



3. A portion of the crust (magnified) , showing an alimen- 



tary and fertile polypite, a spine, and the spiral 

 and tentacular appendages. This figure is dia- 

 grammatic. 



4. A polypite bearing male gonophores. 



5. A monstrous polypite formed by the union of a sterile 



and a fertile zooid. 



6. A polypite in an early stage of growth. After Quatre- 



fages. 



