ZOOLOGY: G. H. PARKER 
451 
the other side decrease in responsiveness. This change has also been 
supposed to be due to changed metabohsm, but, since it appears quickly 
and before a general metabolic change can have occurred, it is probably 
that this too is the result of fatigue in that the food juices from the cavity 
of the tentacles transfuse the walls of these organs and thus reduce the 
sensitiveness of their exterior. Thus none of the elements in the feeding 
responses of sea-anemones imply that these animals are organisms that 
respond as firmly united wholes. 
Retraction, whereby the more delicate parts of the sea-anemone are 
drawn in and covered, is the commonest protective act of this animal. 
Expansion is the reverse of retraction and puts the animal in form for 
full activity. Vigorous mechanical stimulation, most chemical stimuli, 
strong light, and high temperature induce retraction. The presence 
of food in the adjacent water, and water currents induce expansion. 
Oxygen as such seems to have little effect on these reactions. 
Sagartia retracts when left dry by the tide and expands when it is 
again covered by the returning water. Metridium retracts in bright 
dayhght and expands at night. The tidal rhythm of Sagartia and the 
nychthemeral rhythm of Metridium are not retained after the rhythmic 
stimulus is removed as has been claimed for European species by Bohn. 
There is also no evidence of an anticipatory reaction to the tides as 
maintained by Pieron. The retraction and expansion of sea-anemones, 
therefore, give no support to the view that these animals act under 
highly specialized nervous states. 
The form of response which more than any other involves a sea- 
anemone as a whole is creeping. But even this form of activity can be 
accomplished by the pedal half of the animal. To repeated stimuli 
sea-anemones quickly adjust themselves rather by a process of adap- 
tation then by one of exhaustion. Yet they have been found to show no 
evidence of associative capacity. They are animals whose momentary 
conditions are dependent upon the combined stimuli of their immediate 
surroundings rather than forms that are greatly influenced by their 
past history. And in consequence of this their unity is not of a pro- 
nounced type. They are more in the nature of a sum of parts than they 
are organic units such as we are familiar with among most of the higher 
animals. 
The extended paper will be published in the Journal of Experimental 
Zoology. 
