HYDRA. 103 



There seems a natural delicacy incident to the whole tribe in confine- 

 ment ; nor have I been able to preserve any adult individual above a month 

 in activity. 



This specimen being removed from its vessel on August 25, a quan- 

 tity of brownish matter like dust remained at the bottom. Subjected to 

 the microscope, it proved an host of animated creatures in quick and varied 

 motion. 



But to the naked eye they were hardly perceptible, — the merest 

 specks, infinitely minute, — nor by an ordinary lens could their propor- 

 tions be discovered. 



Higher powers, next resorted to, shewed them white, opaque, and 

 fleshy, tending to an elliptical form, though very mutable, one extremity 

 generally broader than the other, with which each individual made its way 

 among the multitude of its fellows. 



Although such be the real and natural figure of the animal in vigour 

 and perfection, some already betrayed incipient alteration in assuming a 

 broader oval, contracting middle, a globular shape, becoming a thick 

 spherical triangle, or exhibiting other irregularities. Nothing strictly an- 

 gular was seen among them. 



All were crawling below with a quick, smooth, lively motion. The 

 body seemed consistent and soft, evidently yielding in pressure through 

 the crowd. No cilia or other external organs, though probably present, 

 could be detected ; for, perhaps the magnifying powers were insufficient. 



On the whole the animals obviously participated of the nature of the 

 PlanulcB, above described as belonging to the Sertularia ramea, and of 

 the others whereof we have yet to speak, as the origin of many zoophytes. 

 — PI. XVI. fig. 2, enlarged ; fig. 3, magnified. 



After the lapse of other forty hours, the subjects of figs. 2 and 3, 

 seemed of twofold composition, as consisting of a lighter margin now sur- 

 rounding a darker interior portion of corresponding form, — previously, the 

 whole had a uniform homogeneous aspect. The shape of others had also 

 become considerably modified ; but whatever the outline of the exterior, 

 that of the interior always corresponded : if the nucleus or inner darker 



