MEDUSA BIFIDA. 125 



fig. 8, having become more amply developed, as in fig. 9, were under such 

 vehement exertion at noon, soon after obliteration of the tentacula, that 

 I felt impatient for the arrival of my artist to delineate the whole subject 

 ■while yet entire, which he accomplished. — Fig. 9. Accordingly, two to- 

 gether were liberated just as the drawing was completed. After struggling 

 severely, they were free of each other. Many days sometimes elapse 

 before dissolution of the roll as previously observed. 



When a drawing of Plate XX. figs. 6, 7, was begun, the lower part 

 of the roll was merely a smooth swelling whirl ; but previous to comple- 

 tion of that and another, the conversion of the whirl to an early embryonic 

 Medusa was perceptible. In nine days the whole Medusas of this subject, 

 fig. 7, were liberated, leaving the hydra free. 



The period is irregular, as may be readily supposed from the unequal 

 numbers composing the roll. I could not ascertain that above seven 

 strata ever came to perfection in Plate XX. fig. 15. But in others they 

 exceed twenty. , 



In proportion to the Medusae liberated from the expanding conic 

 frustum its dimensions are gradually reduced ; but the symmetry of the 

 sustaining bulb is improving, and its tentacula are extending. Their pro- 

 gress is alike variable ; also certain parts are generated, which afterwards 

 disappear. 



Several Medusae having escaped from Plate XX. fig. 8, only three or 

 four remained on March 31, the bulb now becoming a hydra with extended 

 tentacula. In five more days the hydra was symmetrical, with a long spur 

 issuing from the side, fig. 9, which disappeared subsequently. In other 

 three weeks, a young hydra had been generated, and on May 16 it was 

 nearly as large as the parent, a, from which it had withdrawn, fig. 10. 

 Fleshy portions, such as fig. 11, enlarged, promised embryos, but they dis- 

 appeared. The hydra of this subject, figs. 9, 10, a, survived 125 days 

 after being freed of the Medusa. It had also generated several young ; 

 but having gorged itself with food, it was lost accidentally. 



If the period occupied by the changes is irregular in point of dura- 

 tion, the ultimate issue is definite. For example, the tentacula crowning 

 a waved roll or cylinder implanted on a simple bulb, Plate XX. fig. 2, 



