1 68 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Skr. 



represented by the following figures fused : fig. 23; figs, i 

 and 2, but at that time the colony represented in fig. 2 had 

 the appearance of fig. 8 without the coating; fig. 3 and a 

 colony much like it, except that it had black cloacal orifices ; 

 figs. I and 3 ; figs. 8 and 9, but at that time the latter colony 

 looked more like fig. 8 without the white coating but with 

 whitish cloacal orifices; fig. 8 and another colony of nearly 

 the same, and sometimes of exactly the same color; fig. 9 

 and another colony of exactly the same color; figs. 10 and 

 II; figs. 14 and 15. Similarly, the colonies represented by 

 the following pairs of figures did not fuse though they had 

 ample opportunity: figs. 9 and 11 ; figs. 10 and 14. 



The fusion is not entirely determined by vigor of growth, 

 though of course the colonies must be increasing in size; 

 for the absence of fusion between two very vigorous colonies 

 and also between one very vigorous and one rather weak 

 colony was observed, though the weak colony might later 

 fuse with another one. Nor does the presence of sexual 

 reproduction, or the fact that in one colony the zooids are 

 full grown, while in the other they are ready to die, influence 

 the process. It cannot even be said that colonies that have 

 been in contact for thirty-three days without fusing would 

 not have fused if left in contact longer; for two colonies 

 that were in contact for twenty-eight days without fusing 

 fused on the twenty-ninth day. But it is certain that some 

 pairs fuse very much more easily than others, and also very 

 probable that in many pairs fusion would never occur, no 

 matter how long the colonies remained in contact. 



The general conclusion mentioned above, that it is the 

 degree of similarity between isolated colonies and not their 

 separate existence that determines whether they shall compete 

 juith each other for a substratum to grow on or whether they 

 shall fuse, \^ not without some general importance. We are 

 usually in the habit of considering that competition depends 

 solely upon the existence of several separate individuals, 

 living in close proximity to one another; and that it is 

 strongest between those individuals or species whose habits 

 and needs are most similar. But in some communities of 



