160 ZOOPHYTES. 



Many have a slight curve or elbow in the middle ; and the orifice is gene- 

 rally oblique. 



The hydra is light grey, provided with about 22 muricate tentacula, 

 surrounding the low closed orifice of the central pouch. It is very lively, 

 protruding a long and slightly tapering neck far beyond the mouth of its 

 cell, which is extremely transparent, and it retreats suddenly within. — 



Fig. 4. 



While in vigour, numerous hydrse, in all their vivacity, fringe the 

 branches of this product ; but their existence is brief in confinement ; and 

 when internal decay has consumed the pith, along with the living tenants 

 of the cells, only a diaphanous skeleton is left behind. 



Large and peculiar vesicles, alike difiicult to be described and repre- 

 sented, are borne by the Sertularia rosacea, without any regular distribu- 

 tion. In some places they are single, elsewhere rather in pairs, or some- 

 times several in a line are crowded together ; and they are interspersed with 

 living hydra; on the same portion of the specimen, fig. 5. Their trans- 

 parence is extreme, for they are scarcely visible by the microscope. All 

 are fashioned somewhat like a tall vase, ribbed longitudinally by lines a 

 little darker than the sides. Each enlarges upwards from its origin, and 

 near the summit contracts by a mucronate smaller orifice, formed of points, 

 shaped very differently in different specimens. — Figs. 7, 8, 9, 10. 



Prolific vesicles occur in the summer months, May, June, and July, 

 when they contain three or four white or yellow spherules above, towards 

 the widest part, and sometimes appear sustained on a pillar within, fig. 9. 

 The spherules unfold as a diminutive planula, not exceeding the fourth of a 

 line in length, which issues from the orifice of the vesicle. These creatures 

 are occasionally seen traversing their prison as they approach maturity, 

 apparently seeking an exit, which is precluded by an invisible barrier. 

 Having departed, they prove, like others, of variable form, move, be- 

 come stationary, distorted, and undergo the wonted metamorphosis. — 



Figs. 11, 12. 



The planulse, from specimens obtained on May 1, had all metamor- 

 phosed to different stages on the 11th. Some consisted of a stem with a 



