PLANT-ANIMALS, OR ZOOPHYTES. 165 



species. The male and female are sometimes pro- 

 duced on the same polypary, but more commonly; 

 perhaps, any given polypary is either male or female, 

 as far as its reproductive buds are concerned, although 

 Mr. Hincks thinks that the cases in which both male 

 and female are mingled on the same shoots are much 

 commoner than has been supposed. 



After impregnation, the ova in the female capsules 

 pass through intermediate stages, and at length 

 become resolved into a granular mass, which by 

 further development, becomes an elongated embryo 

 (planula), which escapes from the capsule into the 

 water, and temporarily enjoys a free existence, but it 

 is the embryo which becomes free and not the sexual 

 polype, as in the case of the veritable free swimming 

 polypes. The liberated embryos have a double 

 coating, or membrane, and the outer surface is almost 

 always covered with vibratile cilia, or moveable hairs, 

 by means of which their progress in the water is 

 directed. Afterwards the body enlarges at one end, 

 and a thin horny, or chftinous, film is formed over a 

 portion of the surface, then its movements slacken , 

 and at length cease, the cilia disappear, and the 

 embryo becomes attached by the enlarged end, 

 which flattens out into a disk, whilst the rest of the 

 body stands erect in its centre. This is the first 

 evident step towards the foundation of a new colony. 

 The disk of attachment by-and-by becomes lobedi 



