LOCOMOTION IN YOUNG PECTINATELLA. 247 



days. It shows further increase in size and a greater degree of 

 locomotion of each of the colonies. 



Fig. 9 represents the colonies three days after Fig. 8. Marked 

 changes have occurred ; colony A has more than doubled its 

 size and has divided into two parts : A 1 and A' 2 , each of which 

 is moving ; A 1 is growing and migrating ; B" 2 has just divided 

 into two parts : B 2A and B 1 -". 



Fig. 10 represents the colonies two days after Fig. 9. They 

 are in a state of rapid growth as indicated by their increased size 

 and their definitely-lobed margins. 



Fig. 1 1 represents the colonies two days later, indicating im- 

 portant changes. Colony A 1 is divided into two : A IA and A 1 -' 1 , 

 which are moving apart. Colony A 1 is much enlarged and 

 divided into A 2A and A 2 -' 2 . Colony B l has become deeply lobed. 

 Colony B"- 1 is moving and preparing to divide. Colony B' 2 -" 2 has 

 divided into colonies B 2 '- l and B" 2 -' 2 -' 2 . 



Fig. 1 2 represents the conditions three days later. It shows 

 increase in size of each of the colonies, and further division of 

 colonies A 2 - 1 , A 2 ' 2 , l and B 2 - 1 . Also a part of colony B 2 -- has 

 fused with a part of colony A 2 -' 2 . From this time forward the 

 locomotion of the individual colonies cannot keep pace with their 

 growth. Hence as the colonies divide and move apart they 

 come in contact with other colonies with which they fuse. 



Fig. 13 represents the colonies two days after Fig. 12. A 

 number of the colonies are literally running together. 



Fig. 14 represents the conditions after an interval of three 

 days. It shows marked growth in every direction. All but a 

 few outlying colonies are united in a single mass. 



Fig. 1 5 represents the colonies three days later. They are 

 forming one continuous mass, which is not only expanding its 

 area rapidly, but also is thickening perceptibly, especially in the 

 middle. The latter change is due to the heaping up of the 

 secretion of the under surface of the colonies. 



This study of the young Pectinatella colonies shows very con- 

 clusively that they possess the power oi locomotion. This power 

 is definitely associated with the phenomena of growth and divi- 

 sion. The increasing size of a colony causes it to divide. The 

 fact that young Pectinatella colonies multiply by fission was first 



