SERTULARIA. 201 



specimens, a stump, which is apparently an integral portion of the stalk of 

 the twig interposes on each side between two hydrse. — Plate XXXIX. 

 fig. 2 ; twig and hydrae, enlarged. 



Vegetation. — ^The vegetative faculty of this Sertularia is conspicuously 

 displayed. A section three inches long having been deposited in a vessel 

 on September 24, the pith of the middle decayed, but twigs issued from 

 the sides, both above and below the vacuity ; and from the extremity of 

 the section also ; hydra; were generated from the twigs, the first of them a 

 month after the section had been deposited, therefore requiring that inter- 

 val for maturity. 



The upper extremity of an artificial section is likewise prolonged by 

 reproduction, when new t-wigs originate from it, resembling the slenderest 

 needles. A stem thus regenerated or prolonged, had 13 series or sets of 

 such needles. Of these seven bore prolific cells ; but none had above two. 

 Where progressive increment is advancing, prominences on the stem de- 

 note incipient twigs, whose gradual growth admits the evolution of cells. 

 The hydra first displayed is from that cell of the twig nearest the stem of 

 the Sertularia, and the second hydra from the cell next to the first. There- 

 fore, the most distant embryo is the least mature. 



Propagation. — The stem of this product, which rises singly, is en- 

 vironed by ovoidal vesicles, with an orifice somewhat heart-shaped, immedi- 

 ately lower than the convex summit of the vesicle, and almost invariably 

 opening inwards. The vesicle stands in the axilla formed by the twig 

 with the stem.— PI. XXXIX. figs. 3, 4. 



A single yellow embryo originates here, so large that there seems no 

 room for more. It is evolved as a planula, surpassing the size of any that 

 I have seen issuing from a Sertularia, for it is nearly the twelfth of an inch 

 in length. 



Five specimens, crowded with vesicles, were obtained on Novem- 

 ber 1 9. Sometimes these are in such profusion that the stem seems of un- 

 usual thickness. Here all were of the same ovate formation, the orifice 

 inwards, and each vesicle containing a single embryo. Several having 

 been set apart, planulae of a fine yellow colour, and of the preceding ample 

 dimensions, appeared in the vessels on November 22. — Figs. 5, 6. 

 VOL. I. 2 c 



