246 ALICE W. WILCOX. 



give rise to young colonies. The colonies on one gate I observed 

 regularly at twenty-four hour intervals for a period of six weeks 

 from June 8 to July 21. The observations were recorded in a 

 series of forty-three outline drawings made to scale, showing the 

 colonies in their actual position in relation to certain fixed lines. 

 A selected series of fifteen of these figures is reproduced to illus- 

 trate this paper. 



In each figure, the unbroken outlines represent the position of 

 the colonies on the date indicated, and the broken outlines their 

 position the previous day. The two straight lines, crossing each 

 other at right angles represent the fixed reference lines on the 

 flood-gate. 



Fig. i represents two small colonies, A and B. Colony A has 

 just come out of its statoblast and become attached. Colony B 

 is somewhat older and about three times as large as A. 



Fig. 2 represents the same colonies two days later. Their 

 size is not perceptibly increased, but both colonies have moved 

 to the right and A has approached a little nearer to B. B shows 

 a slight constriction preliminary to division. 



Fig. 3 represents colonies, A and B, after another interval of 

 three days. Both colonies have increased in size and are coming 

 still nearer together. B is becoming definitely lobed. 



Fig. 4 represents the conditions one day later. Colony A has 

 migrated back toward its original position. Colony B has divided 

 by fission into two parts, J5 1 and B~. 



Fig. 5 represents the colonies the following day. Colony A 

 is still shifting its position slightly, but without increasing in size. 

 Colonies, B 1 and B", are already beginning to move apart and to 

 change their position in relation to colony A. 



Fig. 6 represents the conditions seven days later. After a 

 period of comparative rest colony A has moved to a new position 

 and increased in size. Colonies, B 1 and ~, are still changing 

 their absolute and relative positions. 



Fig. 7 represents the colonies three days later. Each has 

 definitely enlarged and changed its position somewhat. B 2 has 

 moved entirely off its position of the day before as shown by 

 comparing the even and broken outlines of the colony. 



Fig. 8 represents the conditions after another interval of three 



