18 ANTHOZOA IIYDROIDA. 



its oriofin, I had named it Animalculum tintinnahdum, from 

 its general resemblance to a common hand-Lell, for the purpose 

 of recognition. This creature is whitish, tending to transpa- 

 rency, about half a line in diameter ; the body is like a deep 

 watch-glass, surmounted by a crest rising from the centre, and 

 fringed by about twenty-three tentacula pendant from the lip 

 below. These are of muricate structure, or rough, and con- 

 nected to the lip by a bulb twice their own diameter. The 

 summit of the crest unfolds occasionally into four leaves, and 

 four organs, prominent on the convexity of the body, appear at 

 its base. When free, the animal swims by jerks, or leaps 

 through the water, or drops gently downwards ; it is invited 

 to move by the light, and it has survived at least eight days. 

 Then it disappears; at least, I have not been able to pursue its 

 history longer. No other product has ever issued from the 

 vesicles of the Sertularia dichotoma."** 



This metamorphosis, in the same or nearly allied species, 

 has been traced with the hand of a master in anatomy and 

 physiology, by Van Beneden, but it suffices for our purpose to 

 state that his observations establish those of the Scottish 

 naturahst. Originating in the pulp of the parent, the germi- 

 nating bulb goes through a series of changes. At first it is 

 vesicular and amorphous, but we soon perceive, from little 

 knobs pullulating from the upper disk, and from the body be- 

 coming more isolated, a faint portraiture of the future polype 

 in the ovisac or vesicle, whence this embryo is about to issue 

 under the guise of a minute Medusa, to float at freedom in the 

 circumfluent waters. These changes will be easily understood 

 by a selection from the figures given by Van Beneden. (Fig. 

 3 — 9.) What is very remarkable in these embryos is, the ex- 

 istence of an organ at the base of each tentaculum, in which 

 appear to be united the sense both of sight and hearing, for it 

 has the same structure as the eye and the ear in the lower tribes 

 of invertebrated animals ; f and, moreover, there are found in 

 these embryos distinct bundles of muscles, and nerves with 

 their ganglions, — all of which disappear in the adult. We 



* Edin. New Phil. Joum. xxi. p. 91-2. 



f Les Campanulaires, p. 26-7. — The medusan embryos of the Tubularise have not 

 these organs. Les Tubulaires, p. 35. 



