1 66 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Skr. 



to be some active antagonism between the colonies, which 

 prevented a union even when two cut surfaces were placed 

 in contact. 



In the case of Botrylloides, however, a better success was 

 encountered. Only two colonies of B . gascoi were at the 

 writer's disposal; but one of these had been collected a week 

 earlier than the other, thus increasing the probability that 

 they were not parts of the same colony. A union of these 

 two individuals was easily obtained by grafting. The vessels 

 in the two pieces joined with each other, and the zooids 

 from both helped to form the same system. To test the 

 reason for the union in this case, other pieces from the same 

 two colonies were taken, and allowed to grow toward each 

 other naturally. When they met the two colonies fused, 

 thus showing that the reason that the graft took in this case 

 was not because of a particularly favorable operation, but 

 because there was no antagonism between the two colonies. 



Similar results were encountered Wiih. B otrylloides rub?'um. 

 There was no difficulty in obtaining a union of two colonies 

 either by grafting or growing towards one another. Although 

 a fusion was obtained in only three cases, still it occurred 

 in the majority of the trials, and was also encountered 

 where the growth was vigorous enough to lead one to expect 

 it. Therefore in spite of the limited number of observa- 

 tions, the conclusion seems justified that: On the whole, 

 neighboring Botrylloides colonies behave very differently 

 towards each other from Botryllus colonies. 



A hint as to the cause of this difference may be found in 

 the character of the variation in the two genera; for, while 

 in Botryllus the variation could hardly be greater, in 

 Botrylloides it is quite limited. All of the six or seven 

 colonies of Botrylloides gascoi seen, had, except when 

 gestivating,^ exactly the same color pattern and practically 

 the same color. Fully a hundred colonies of Botrylloides 

 rtibruni were examined, and no variation at all comparable 

 to that in Botryllus encountered. The color pattern varied 

 but little, and the color only from a yellowish to a deep 



1 An account of this aestivation is awaiting publication elsewhere. 



