REPRODUCTION BY GEMMULES. 425 



thin, and fringed by a border of active cilia, forming 

 beautiful objects under the microscope. They traverse 

 the water readily in all directions, ascending, de- 

 scending, or revolving as if on an axis, with marvel- 

 lous ease and most graceful evolution. 



On isolating one of these gemmules, it is seen 

 after a few days to remain stationary, and speedily to 

 become affixed to the spot whereon it has rested. 

 In a few days more a polyp becomes developed, 

 displaying itself from a short tubular orifice at one 

 extremity. Next, a wing is formed by development 

 from the side, which is the commencement of a new 

 cell wherein a second polyp originates, which, having 

 attained maturity, is displayed along with its elder 

 companion ; and from the transparency of these new- 

 formed cells, it is easy, at this period, to examine 

 completely the form and organization of the animals 

 within, an advantage not permitted in the adult, 

 owing to the darkness and opacity of the polypary. 

 From the sides of these first-formed cells, others soon 

 begin to sprout, which, as they become complete, and 

 furnished with their enclosed polyps, give rise in their 

 turn, in a similar manner, to a third generation 

 these again to a fourth, and so on, until the symme- 

 trical dimensions of the leaf-like polypidom are ulti- 

 mately attained by a continuance of the process. 



The growth of the polyp aries, which are thus 

 densely populated, is thus seen to be effected by the 

 progressive addition of new cells around the circum- 

 ference, those occupying the margin being of course 

 the most recently formed ; and, indeed, the latter are 

 not unfrequently found inhabited by the living ani- 



