HYDRA 261 



In regard to the first question we can only say that in the 

 attached condition animals are no less able to live and multi- 

 ply than in the free-living state. The sponges and the corals 

 that help to build oceanic islands, and the Bryozoa that are 

 found on every sea-coast and in nearly every lake and pond 

 are eminentlj- successful groups. 



In regard to the changes in form which accompany sessile 

 life more may be said. First, the attached or sessile animals 

 tend to grow, like the trees, by buds. The new individuals, 

 budded from the old, may in some cases separate from the 

 parent individual and swim away to become attached again at 

 a distance, or they may remain as permanent branches. By 

 repetition of the budding process a tree-like form may be pro- 

 duced, as in the corals. Secondly, attached animals, since 

 they do not move from place to place, have less need of sense- 

 organs with which to find the waj''. Consequently, we often 

 find attached animals devoid of organs of hearing and even 

 of sight, although the touch reaction is always present. As 

 a result of the reduction of sense-organs on the head, the brain 

 has become greatly reduced. Of course all locomotor organs 

 have become rurlimentary and the muscular sj'stem has corre- 

 spondingly become very rudimentary. These reductions in 

 turn have affected the nervous system so that it has become 

 greatly simplified. Thirdly, since attached animals are not 

 able to hunt for their prej', they must take what is wafted to 

 them by currents in the watei\ Furthermore, they are supplied 

 with a mechanism for making whirlpools the apex of which 

 leads to their mouths. This mechanism often consists of 

 tentacles covered with cilia, the beating of which creates the 

 vortex whereby small particles of food are drawn into the 

 mouth. Finalljr, the methods of reproduction have been 



