ANIMAL METAMORPHOSIS. 89 



complicated. These animals, which by those unacquainted with 

 their true nature, are often mistaken for seaweeds, consist of a 

 number of hydra-like creatures, which, instead of separating from 

 each other, and living an independent existence, like the pond 

 Hydra, continue to multiply by budding, the separate members 

 being united together into a plant-like colony by means of a 

 common flesh or csenosarc. In many of these organisms there 

 are two distinct sets of zooids : one devoted to the duty of pro- 

 viding food for the colony ; the other generative buds or gono- 

 phores (whose office is the production of ova and spermatozoa), 

 and are altogether unlike the nutritive zooids. In some cases they 

 remain permanently attached to the parent organism, as in the 

 Sertularia or sea-firs ; but in others, the generative buds become 

 detached from the colony, and develop into free-swimming, bell- 

 shaped organisms, which are identical, structurally, with the jelly- 

 fish, or Medusae, and sometimes attain a comparatively gigantic 

 size ; individuals having been found as much as seven feet across, 

 with tentacles over fifty feet long, though the parent from which 

 they were produced was only a minute fixed polype, not more 

 than half-an-inch in height. At certain seasons of the year, these 

 huge jelly-fish drop from their under surface a vast number of 

 minute ova, which, after passing through the planula stage, settle 

 down upon the rocks, and develop, not into the free-swimming, 

 bell-shaped organism, by which they were actually produced, but 

 into the plant-like, rooted zoophyte from which the buds were ori- 

 ginally given off. 



Sea-anemones are also able to increase in three ways : either 

 by fission, gemmation, or, as is most common, by hatching the 

 young from ova within the body of the parent. Nothing can be 

 more unlike the parent Actinia than their minute embryos, some 

 flattened, some elongated, and others with irregular prominences 

 as if composed of two or more unequal spheres, but all are 

 covered with cilia, and it is not until they are eighteen or twenty 

 days old that the rudiments of tentacles are visible, and they settle 

 down and gradually assume the adult form. By carefully watching 

 an anemone, the young may often be seen coming out of the 

 mouth of the parent, sometimes in the shape of little ciliated 

 Swimming bodies, but more often they are hatched within the 



