ZooL.— Vol. III.] BANCROFT— COMPOUND ASCIDIANS. 1 83 



VII. Summary. 



1. The mortality of young colonies is very great. 

 Those that survive appear to be selected on account of their 

 greater vigor of growth. 



2. The only enemies proper of Botryllus discovered 

 are crabs. These were seen to eat Botryllus and refuse 

 Botrylloides. 



3. In its struggle for a substratum with other competing 

 organisms, the only resource of Botryllus is rapidity of 

 growth. The edges of the colony grow most rapidly and 

 the center dies first. 



4. Colonies of Botryllus did not sestivate nor hibernate. 

 Some were kept under observation for nearly seven months. 

 Their maximum length of life seems to be less than a year. 



5. The ground-color of each zooid changes during its 

 life. The color patterns, when present, are quite indistinct 

 when the zooid first becomes adult; but, as it grows older, 

 the patterns become more distinct and complex. 



6. The growing edge of the colony may sometimes 

 have a different color from the center. 



7. The size and color of the zooids vary very much in 

 the same colony at different times. 



8. Colonies of Botryllus reared from larvae extruded 

 by the same colony present differences comparable in all 

 respects to those between described species. Therefore 

 all European and eastern North American described species 

 should be lumped into one. 



9. Certain of the color markings exhibit discontinuous 

 variation, while others do not. 



10. Unrelated colonies of Botryllus will not fuse with 

 each other and cannot be grafted. 



11. Unrelated colonies of Botrylloides do fuse when they 

 grow toward each other and meet. There is less variation 

 in this genus than in Botryllus. 



12. Pieces of the same colony in both genera fuse very 

 easily. 



13. Sister and brother colonies of Botryllus sometimes 

 fuse and sometimes do not. 



