166 ZOOPHYTES. 



passing the natural increment. They are then pale, and bear some short 

 spinous twigs at distant intervals, from whence hydrse are generated. 



Propagation. — There is no absolute uniformity in the size, shape, or 

 colour of the vesicles borne by what I consider the type of the Sertularia 

 halecina, if this distinction shall be allowed. 



All the preceding specimens, of December 31 [p. 163], were laden 

 with vesicles, Plate XXVII. ; and what is now to be remarked in regard 

 to them, has been also witnessed in many others. 



The vesicles were of diverse characters, even of irregular shape ; gib- 

 bous, or with a hump on the green parts of the Sertularia, Plate XXIX. 

 figs. 3, 4 ; likewise grey ovoidal vesicles on the grey parts, fig. 5. But 

 some green specimens have both gibbous and ovoidal vesicles, as figs. 7, 8. 

 The vesicles shewn on fig. 6, were borne along with ovoidal vesicles ; and 

 the grey parts bore such as resembled figs. 9, 10, on the same branch. 



The different figure of these vesicles is seen still more distinctly in 

 delineations of them, from green specimens of the Halecina and its cog- 

 nates.— PI. XXX. fig. 1 ; PI. XXXI. figs. 4, 5, 7. The orifice of the 

 one is in the hump ; of the other in the extremity. 



It is obvious, therefore, that vesicles of different formation are borne 

 by the Sertularia halecina. 



The vesicles of some specimens are green exclusively. — PI. XXVII. 

 Of others they are exclusively yellow. — PI. XXVIII. fig. 1. The grey 

 parts bear white vesicles. 



As usual, the vesicle is the matrix wherein several planulae, from 

 whence its colour is derived, are brought to maturity ; their numbers are 

 commonly two, three, or four, in each. 



The specimen, PL XXVII., produced both green and white planulije, 

 undistinguished by any features to render them remarkable. Many of the 

 ffreen were crawlinsr in a smaller vessel, a, on the 13th of January, from 

 which I shifted the specimen next day, to a wide shallow vessel, b. Many 

 also appeared in the latter, on the 17th ; and they had augmented to above 

 100 on the 18th, all pale green, A group, on the 20th, consisted of the pla- 

 nulae, in every stage of animation and incipient metamorphosis, PI. XXIX. 

 fig. 11 : the natural form being a, b, c ; two others were contracting, and 



