108 ZOOPHYTES. 



veiling buoyancy accompanying incipient metamorphosis, or whether by 

 ascending the sides. Frequently there are scarcely any remaining below ; 

 but numberless specks, denoting their presence, may be also sometimes 

 seen at the bottom, while the scum is composed of multitudes above. 



Having shifted a Medusa of the former species from a capacious ves- 

 sel, I poured off almost the whole water, leaving innumerable planula? 

 among the residue. This residue being next emptied into another, a 

 smaller vessel, four inches wide by two deep, the bottom was entirely co- 

 vered by planulse. From the vast legions below I was apprehensive of 

 decay, however, all remained vigorous : and in three days numbers were 

 swimming throughout the water. In three days longer, the surface of the 

 water was overspread by a film resembling cambric paper, obscuring the 

 whole contents at the bottom. Extraordinary myriads of planulse were 

 in the vessel, so that, for more security, to avoid vitiation, and to give 

 the animals greater scope, by increasing the quantity of the element, and 

 to prevent interruption of the course of observation, I sunk this smaller 

 vessel in one of much larger dimensions, wider and deeper. As the latter 

 was gradually replenished, a compact circular scum, equalling the diameter 

 of the former vessel, rose entire and unbroken, composed wholly of 

 planulse. 



Though I describe it as wholly of planulse, the scum consists also of 

 a large proportion of glutinous matter along with them, — another remark- 

 able provision of Nature. 



The progress of that metamorphosis converting an animal of great ac- 

 tivity to one in a stationary condition, seems to be attended with the exu- 

 dation of a glutinous matter from the body. While active this would be 

 of little use, but now it is different in becoming the means of security. 

 Thus, where the animal occurs singly, and the change so far advanced that 

 it adheres, a slight diffusion around the extremity, or point of adhesion, is 

 perceptible by the microscope. 



The secretion of this substance, I presume, is the origin of the tena- 

 cious scum ; and owing to the incalculable numbers crowding the surface, 

 the smallest quantity from each, would produce, when united, a compact 

 matter wherein they might be imbedded. 



