ASCIDIA. 151 



merly indicated originating zoophytes, remained on the internal surface of 

 the vessels. The same followed every future observation : No other discre- 

 pancy being sensible than in the earlier or later interval of their appearance. 

 The Spinula? having continued healthy, active, and vigorous, for a cer- 

 tain time, some of them are seen with the head applied to the bottom of 

 their vessel, and the tail upright, stationary, and as if enjoying a state of 

 perfect repose, in this inverted erect position. Meantime, the front is enlarg- 

 ing : it seems hollow, the margin is dividing into angular projections, and 

 incipient adhesion, by one or more of them, to the glass, ensues. Now, the 

 animal is no longer tranquil : its violent struggles testify that it is unwit- 

 tingly or unwillingly arrested : its exertions are vehement to be free. At 

 this juncture, the vibrations of the tail become so rapid, that, like those 

 of a cord in tension, its figure is hardly discernible by the eye. 



At length quiescence follows ; some diffusing matter escapes from 

 the margin of the flattened head, and the spinula is rooted irreversibly to 

 the spot. — Fig. 6. 



Some analogy will be doubtless recognized here between the circum- 

 stances now related, and those concomitant on originating zoophytes, so 

 largely described above. I leave further prosecution of the parallel, and 

 its explanation, to more skilful physiologists. 



But in respect to the subject before us, an evident alteration suc- 

 ceeds in a few days. A dark, solid nucleus, is substituted for the adhering 

 head of the Spinula ; the tail has vanished ; a transparent marginal diffu- 

 sion surrounds the front where applied to the glass, towards the circum- 

 ference of which are distributed 26 or 28 flattened radicles, diverging from 

 the nucleus as a centre. — Fig. 7. 



As the nucleus consolidates, two nipples, with quadrangular orifices, 

 rise from the surface, while the radicles below, gradually attenuating, dis- 

 appear from view ; and the transparent diffusing matter forms a skinny 

 environing ring of the basis, — a complete metamorphosis has been accom- 

 plished ; — the Spinula is transformed to an Ascidia, — such as the Ascidia 

 papilla above described. 



It may be credited, however, that this process is not as rapid as the 

 description ; on the contrary, its advance is slow and gradual. Sometimes 

 the spot denoting the elements of a nascent animal has formed within 



