SERTULARIA. 171 



In respect of time, the progress of metamorphosis seems irregular, 

 nor am I aware of any precise rules by which it is governed. Sometimes 

 the circular spot speedily follows the departure of the planula from its 

 prison. About 50 planulse appeared on the bottom of a vessel with ve- 

 sicles on the 4th of November. All these had ascended the side next 

 day, and almost as many replaced them below. Numerous circular white 

 spots with spines appeared on the 7th of the month, both on the sides and 

 on the bottom of the vessel. 



3. Until some learned naturalist, by the aid of the skeleton, and of 

 living specimens, shall determine the absolute distinctions of the species 

 here assumed as the Sertularia halecina, the following remarks are meant 

 as generally applicable to the whole indiscriminately. 



All rise from the root by a darker or lighter white, green, or brown 

 stem, which consists in adults of aggregated tubuli. Renovated extremi- 

 ties or recent generations are pale green or white, the rest of the speci- 

 men being some hue of the preceding colours. The whole subordinate 

 parts are in alternate arrangement. Originally the twig hardly rises above 

 the larger member sustaining it : and it may remain alike low at a greater 

 age. But it also appears so much prolonged as to exhibit from two to 

 seven frills. 



The hydra issues from the highest of these frills ; but it is not retrac- 

 tile entirely within the tubular part of the twig. It is greenish or white. 

 Adults, or those of larger and older parts, have from 20 to 24 tentacula. 



Hydrae are regenerated from the same twig. A powerful reproduc- 

 tive faculty also generates shoots from the lower extremity of sections con- 

 taining the elements of hydrae subsequently developing on them. 



Numerous green or yellow vesicles of varied form are distributed over 

 specimens. One about 30 lines high, and expanding as much in breadth, 

 was laden by above 400 yellowish vesicles, dispersed over the boughs and 

 branches, with a few up to the very summit on the stem. The yellow of 

 the vesicle in contrast with the green of the other parts, rendered this di- 

 minutive product an elegant type of a fruitful tree. The form of the vesi- 

 cle is much diversified. In some the orifice is at the extremity ; in others 

 a circular lip opens from a prominence near the middle. 



