SEETULARIA. 193 



the third advancing in like manner at a longer interval lagged in the ori- 

 fice, as if more doubtful of safety, but at last committed itself as its com- 

 panions had done, to the water. Now, the sphere remained empty and 

 quite transparent. 



In this way, above twenty planula; forsook their prison during half an 

 hour's observation. — Fig. 7. 



These beings proved very minute, not a third of a line in length, of 

 beautiful vivid yellow, smooth, and uniform aspect as others ; the body 

 thick, consistent, and heavy, tapering slightly with obtuse extremities. 

 They crawled slowly along. 



The vesicles continued discharging multitudes of planulse, rendering 

 that portion of the vessels where they collected yellow from their number. 

 In five days, at least 1200 had gathered together in the bottom of one 

 vessel ; and in two days more, at least 2000 in another. 



Sertularia uber would not have been an inappropriate characteristic. 

 None or very few of the planulae ascended the sides of the vessels. 

 Let us follow the course of metamorphosis. 



Planula? issued from the vesicles on April 7. On the 9th, some ap- 

 ]iarently symmetrical the preceding day had now contracted, much after 

 the fashion of those of the Sertularia fakata. An individual yet exhibit- 

 ing progression was absolutely spherical. 



The period of transformation and subsequent maturity were correctly 

 defined. Vesicles taken from the specimens above quoted having been set 

 aside on the 7th of April, planulaj appeared on the 8th. Circular spots 

 with a spine were seen on the 10th, and on the 17th, hydrse flourished from 

 the cells of the nascent Sertulariaj. The life of the planula, as such, had 

 been thus abridged on the third day ; and from the spot closing its exist- 

 ence, the hydra; had been perfected in other seven. Therefore, within ten 

 days of the planula escaping from the vesicle, it became a Sertularia. 



The spine rising from the spot was yellowish ; the cell enlarging its 

 summit rather of a long campanulate form ; and the hydra had 15 tenta- 



cula. 



These characteristics distinguished the young Sertularise. 

 Compared with the appearance of adults, their form was somewhat 

 VOL. I. 2 b 



