PLATE XVIII. 



Clavatella prolifera. 



Fig. 



1. A colony, magnified. 



2. The same, uatni-al size. 



3. One of the tentacles of the hydranth much magnified. 



4. The free ambulatory medusa (planoblast) as seen when it has attached itself by its suctorial 



discs. 



5. The planoblast viewed from the vertex, showing the radiating and circular canals. «, a 



young medusa-bud ; h, a medusa-bud more advanced. 



6. The ocellus showing its pigment and refracting body. 



7. Extremity of a marginal tentacle of the planoblast showing its two branches, one of which 



is provided with a suctorial disc of attachment. 



8. Vertical section of planoblast showing ova carried in its summit between ectoderm and 



endoderm ; 'a, mouth ; h, h, marginal tentacles. 



9. Young medusa-bud developed from the base of the hydranth. 

 10. Medusa-bud more advanced, marginal tentacles still simple. 



