SEETULARIA. 147 



the 31st of August, which was the latest survivance of any of the first 

 from the spine. 



The contents of the vesicle, though apparently fresh and entire, when 

 discharged in a mass, may prove abortive, as previously stated. The sphe- 

 rules, which should have become planulse, are then retained amidst the 

 albuminous mass, which has been expelled more probably by some aerial 

 expansion, than by an organic animal faculty. 



A residuum frequently occupies the empty vesicle, having discharged 

 its embryonic contents, which is of uncertain nature, fig. 5, a. We can 

 scarcely consider it some organization, generating an'elastic fluid, to burst 

 the pellicle closing the mouth of the vesicle, if there be one, or otherwise 

 promoting expulsion. 



Illustrations of the process of progressive increment are obtained 

 from this species of Sertularia in its earliest stages, besides those aiForded 

 by the young bred from the vesicle. An enlargement appears at the 

 summit of a stalk, which is found to be invested by a delicate thin film, 

 including twin buds composing it. These are unequally advanced ; but as 

 the lower matures, its higher companion forks off, and then another from 

 this latter, the higher. The buds are nascent hydrse in their respective 

 cells, each having, apparently, its own peculiar integument, within the 

 common filmy involucrum. 



Rapid growth ensues. A young specimen, with only a single head on 

 the 4th of October, had acquired six on the 20th, besides a seventh in 

 embryo. Now, it had rose about seven lines. 



A few facts regarding the evolution of the hydra and the regenera- 

 tion of the product, were shewn by older specimens. 



One consisting of a main stem and a single lateral branch, each 

 extending about six lines, was selected for observation on March 9. — 

 PI. XXII. fig. 13. At that time it rose no higher than b. In the even- 

 ing, four of its hydrse, e, e, e, e, displayed themselves from their cells on 

 the stem a, b, and two days after, six on the branch c, d. Thus ten living 

 hydraj then subsisted. But some of them generally lurked in conceal- 

 ment, for the temporary display of a whole colony is rare, though occa- 

 sionally seen, even where very numerous, if circumstances be favourable. 



