SERTULARIA. 149 



the old portion, which, with its collateral embryo, flourished on July 27. 

 They continued displaying themselves until the first of August, when the 

 course of observation was interrupted. 



It is difficult to render this part of the subject more explicit without 

 a series of delineations. But, in abstract, it concentrates in the fact, that 

 the hydrse once replenishing the cells, are replaced after their decay by 

 others. 



Although so powerful a reproductive faculty resides in the Sertidaria 

 polyzonias, no satisfactory issue has attended experiments to obtain it from 

 artificial sections. 



As common to many of the race, prolongations are generated natu- 

 rally from the lower extremity of sections, whether the specimen be 

 flourishing or vacant. 



Among other facts resulting from the preceding observations, it ap- 

 pears : — 



I. That the regeneration of the hydrse, and of defective parts, some- 

 times ensues in the Sertularia polyzonias. 



II. That a period of not less than 58 days may be requisite for bring- 

 ing the dormant principle to maturity as a living hydras. 



III. That propagation of the species is effected through the medium 

 of certain corpuscula generated in the vesicles, which issue forth in the 

 form of active planulse. 



IV. That not fewer than 24 are sometimes contained in a single 

 vesicle. 



V. That the whole contents, as imbedded in a gelatinous substance, 

 may be expelled from the vesicle, and prove abortive. 



Plate XXII. Fig. 1. Sertularia polyzonias. 



2. The same, enlarged. 



3. Branch, shewing the predominance of lateral vegetation. 



4. Extremity of a branch with hydrse. 



5. Relative dimensions of a vesicle, a, and a cell, b. 



6. Prolific vesicle. 



