170 ZOOPHYTES. 



The vesicle, in its most decided form, terminates by an ovoidal extre- 

 mity ; and a prominence, with a circular lip, rises from about the middle, 

 or towards the end, fig. 4 ; living hydrse and prolific vesicles are contem- 

 porary on the same specimens, fig. 5. The vesicles of some specimens have 

 chiefly contained four embryos, fig. 6, which, on maturity, as planulse, seek 

 an exit through the orifice of the circular lip, fig. 7. Having escaped, 

 they traverse their vessel with the swelling head foremost, according to the 

 nature of their race. 



But the regularity of their planarian form is gradually impaired as 

 the vigour of motion relaxes, fig. 9. They become quiescent, and a stem 

 rising from above, indicates a nascent Sertularia. 



On the 16th of October, specimens of this Sertularia, bearing white 

 vesicles, produced planulse of the purest white, very minute, the head much 

 enlarged and obtuse. They swam supine, as most others do. The tempe- 

 rature at the time was extraordinary for the season. Others continued 

 issuing from the vesicles, and after several contained in one of these gra- 

 dually elongating from their globular form, and departing, two of perfect 

 shape remained, which visibly followed through the circular lip, fig. 7, a. 

 The orifice was then first discovered to be there, and not in the extremity, 

 h, as I had conjectured. 



Various white spots were consequent on the escape of the planula?, 

 the first bearing a hydra on the stem, eight days from the date of their 

 production. The same interval elapsed on a different occasion. 



In the course of other observations, specimens with a brown stalk and 

 white vesicles, wherein I thought six embryos could be discovered, were 

 set apart on September 30— the vesicles being of the preceding peculiar 

 formation. Numerous planulae appeared in the vessel in 48 hours, and 

 several spines rising from circular spots on the bottom. Many nascent 

 Sertularijfi, each consisting of a single hydra, were flourishing on the 5th 

 of October. Thus, only six days had sufficed to bring them to maturity, 

 computing from the discharge of the planulse from the vesicle. 



Numbers of planulae were produced on this occasion, all pure white, 

 of fleshy aspect, and not a third or a fourth of a line in length. They 

 swam supine, and when dying without metamorphosis, they decomposed 

 into granulated matter, such as follows the death of the planaria proper. 



