ZOOL.-VOL. III.] BANCROFT-COMPOUND ASCIDIANS. 167 



pure red. Thus it seems that, in Botrylloides, adjacent 

 colonies of ten fuse and do not compete with each other because 

 they are not so different from one another as the colonies of 

 Botry litis. 



4. Fusion of Related Botryllus Colonies. 



In order to still further test the question of fusion in 

 Botryllus, observations were made on colonies developed 

 from larvae extruded by the same mother colony. It was 

 found that some of these colonies would fuse, but others 

 would not, although the conditions were the same in both 



cases. 



The criterion employed, here as elsewhere, for a fusion 

 is the establishment of a common vascular system. Thus, 

 no colonies were recorded as having fused unless the blood 

 could be distinctly seen passing from one to the other in 

 the living colonies. In this way a fusion was observed 

 between twenty-nine pairs of related colonies; while but 

 eighteen pairs of related colonies were observed which were 

 in contact long enough to have fused without doing so. 



Now there can be no doubt that brother colonies are more 

 similar, both so far as color and other characters are con- 

 cerned, than unrelated colonies. Hence, from the observa- 

 tions on Botryllus we have still further confirmation of the 

 conclusion reached in the preceding section ; that it is some 

 similarity in the two colonies which determines that they shall 

 fuse and not compete} But unfortunately it could not be 

 determined wherein this similarity consisted. It is not simi- 

 larity in color which decides the matter, in spite of the small 

 color variation in Botrylloides : for Botryllus colonies with 

 the same and with very dissimilar colors were seen to fuse, 

 and the same variations were observed among the members 

 of the pairs that had ample opportunity to fuse but did not 

 do so. By referring to the figures the amount of these 

 variations may be seen. Among others, the pairs of colonies 



»Jensen(Arch.gesain. Physiol., Bd.LXII) has noted fusion of <9?-3z7<?/rV« under sim- 

 ilar circumstances; pieces of the same individual, and young animals from the same 

 mother fusing, while under other circumstances individuals refuse to fuse. 



