SERTULARIA. 165 



New shoots originate from the most unlikely places. Thus a speci- 

 men above two inches high, quite vacant of hydrae, bore two minute 

 sprigs with hydrae, the longest rising but a line and a half, all of vivid 

 green. — Plate XXX. fig. 11, enlarged. 



Where vigorous hydrae already subsist, the regeneration of others ad- 

 vances in their vicinity — the clear and transparent sheath showing their 

 progressive evolution. Nothing can be more interesting than to witness 

 the rapid refinement of an embryo hydra into perfect configuration, and 

 the display of the organic parts actually completed under the observer's 

 eye. My notice having been directed to a specimen wherein, from the 

 highest of three frills, a dark green globular mass rose prominent as an 

 acorn in the cup : in an hour it became someM'hat clavate, while turned 

 slightly aside, still enlarging without any indications of tentacula. But in 

 another hour these organs became perceptible, through a very delicate 

 transparent involucrum protecting the mass. The head had now pro- 

 truded almost entirely from the frill, and the extremities of the tentacula 

 separating, having improved the symmetry of the parts, they were gra- 

 dually and at length freely unfolded two hours afterwards in their due pro- 

 portions. The new head of the finest green was perhaps the fourth which 

 the twig sustaining it had borne in succession. 



The hydra seems to develope as an enlargement of the summit of the 

 internal pith, and bursts an integument on attaining perfection. Probably 

 the budding Sertularia, like the budding Tubularia, is always thus invested, 

 though extreme tenuity, added to the intimate application of the parts, 

 may conceal its presence. In the Tubularia it is more conspicuous. Na- 

 ture is careful to protect the tender organs of her originating productions, 

 with an external covering suitable to their condition. 



The extent of reproduction is indefinite ; but presuming that succes- 

 sive frills indicate new evolution, it occurs no less than six or seven times. 

 Specimens with three or four such as Plate XXIX. fig. 2 are frequent. 



A vigorous reproductive faculty resides in the Sertularia halecina and 

 its cognates, which is often displayed in another form, by vegetation from 

 the extremities of sections. These coming in contact with a solid surface 

 have a tendency to adhere, and to extend in irregular prolongations, sur- 



