Reactions of yEolosotna to Chemical Stnnuli 51 



to very bright daylight for several days, the number and sizeof the 

 oil globules are considerably increased. Budding and fission. 

 however, show^ a marked retardation. On the other hand, if 

 they are kept in the dark for the same length of time, the appearance 

 of the oil globules undergoes no perceptible change, but the num- 

 ber of budding zooids will be noticeably large. 



The activity of .^olosoma also varies with changes of tempera- 

 ture. When the water is cold their movements are correspond- 

 ingly sluggish. As the temperature is raised the animal becomes 

 increasingly more active until Ehrenberg's description as "ex- 

 tremely agile" becomes peculiarly fitting. The same animals 

 will pass through all stages of relative activity from the early 

 hours of the morning when the water is cool to the mid-afternoon 

 when the temperature is raised by the warmth of the day. 



These variations m activity are correlated with changes in the 

 processes of constructive metabolism. If the animals are kept 

 in cold water they feed very slowly and evidence of reproduction 

 practically disappears. Just the reverse is true when the water 

 is kept warm for some days. 



i^olosoma seems to require certain periods of rest. The rest- 

 ing stage may be observed more generally when the light is sub- 

 dued, and the water is cool. The only movement in evidence at 

 such times is the gentle waving of the setae. The animals lie 

 somewhat extended and approximately straight. If left undis- 

 turbed they may lie in this position for several hours at a time. 



Summary 

 The Action System 



The daily hfe of i^^olosoma exhibits, as has just been shown, 

 certain movements which we may call the "action system" of the 

 animal (Jennings '04). 



Some of these are primarily concerned in the quest of, and the 

 ingestion of food. 



I The beat of the cilia under the prostomium which may draw 

 sample currents of water past the sensory hairs, or may propel 

 the animal in gliding or swimming. 



