ZooL— Vol. III.] BANCROFT— COMPOUND ASCIDIANS. 1 69 



animals, such as are found among the ants and bees, inher- 

 ited instincts or reflexes have brought about a state of 

 affairs in which the individuals do not compete, but co-oper- 

 ate with each other. The community then becomes the 

 competing unit, and it may even happen that communities 

 may combine to form competing units of a still higher order. 

 In the case of trusts and labor unions among men, intelligent 

 co-operation has produced the same result, abolishing, to a 

 certain extent, competition between the most similar com- 

 peting units, and producing units of a higher order. 



Among the fusing colonies of Botryllus we have a similar 

 formation of a higher competing unit, accomplished by the 

 simplest of all means — organic union; and, from the analogy 

 of the other cases mentioned, it is especially interesting that 

 this combination is only possible between the most similar 

 units. 



5. Details of the Process of Fusion. 



Fusion has only been observed when both colonies were 

 of the same age. But it apparently makes no difference 

 what this age is. Fusion was seen to occur between 

 embryozooids, young colonies of all ages, and adult colonies 

 nearly three months old. In all cases the fusion took place 

 in the same way, except that when embr3^ozooids fused 

 there was no tendency towards an aggregation of the zooids 

 into one system (text-fig. i). 



The manner in which the fusion occurs brings us a step 

 further in determining wherein the mutual compatibility or 

 antagonism depends. The final problem, however, remains 

 unsolved. In the first place, it seems necessary that a cer- 

 tain amount of -pressure must exist between two colonies 

 before they will fuse. The fact mentioned above, that mere 

 contact of the colonies is not sufficient, but that they must 

 be growing towards each other if they are to fuse, points 

 in this direction. Further evidence was obtained by a 

 series of observations on isolated pieces of the same colony. 

 These ordinarily fuse with extreme ease. In three of four 

 pairs of pieces examined at one time the fusion occurred 



