Plate 26. 



Late stages in the development of the parasitic generation of Pegantha smaragdina, sp. now 



Fig. 1. Early medusa stage with seven tentacles. The bell margin is indicated by a 

 coronal thickening just oral to the tentacles. X 50. 



Fig. 2. Aboral view of slightly older medusa, with eight tentacles. The ridge repre- 

 senting the future bell margin is now prominent, and the aboral surface is 

 flattened. X 50. 



Fig. 3. Side view of still further advanced stage. The general outline is now flattened. 

 There are nine tentacles of different sizes, x 50. 



Fig. 4. Aboral view of an older medusa. The typical medusa outline has been assumed. 

 There are now ten tentacles. Otocysts have been developed (one per marginal 

 lappet) and the marginal lappet zone has increased in width, x 35. 



Fig. 5. The oldest stage taken. There are two otocysts in some of the lappets. Pe- 

 ronii are developed. From a specimen stained in borax-carmine. X 35. 



Fig. 6. Early stage in the development of an otocyst, in optical section ; (ec) ectoderm, 

 (en) endodermic core of future sense organ, the position of which is marked on 

 the exterior by a slight prominence. No otolith is yet formed. X 250. 



Fig. 7. Twin otocysts (oc). In only one has the otolith been developed; (en) endo- 

 dermic core, x 350. 



Fig3. 8, 9. Two successive stages in the development of otocysts (oc) and otoliths. 

 x 350. 



Fig. 10. Tentacle and peronia (pr) of the specimen shown in Fig. 5. X 100. 



