174 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



was such a composite system observed. But one would 

 not expect to find it frequently; for in a composite colony 

 the two fused colonies would in general occupy different 

 regions. Furthermore, since they were all growing rapidly 

 the new systems would usually be formed from the buds of 

 zooids which had belonged to the same system, and it would 

 happen but occasionally that the two systems were so close 

 together that, when the next generation was developed, 

 zooids from both systems would come together to form a 

 single one. Accordingly, the negative evidence is not 

 weighty, and one must therefore conclude that when two 

 colonies have fused, the two kinds of zooids behave toward 

 each other, so far as the formation of systems is concerned, 

 exactly as if they had ahuays belonged to the same colony. 



(b) Correlation in Growth and Reproduction. 



This is subject to minor variations, but in the main it is 

 remarkably constant. It has long been known that all of the 

 zooids present in the same colony are not only of the same 

 generation, but in the same stage of development. They 

 all die together, and all develop their buds at about the same 

 rate. If any^of them contain ova or embryos, usually all of 

 them do; and all extrude the larvae at about the same time. 

 It was found that when two pieces of the same colony or 

 from two colonies, whose zooids were not in the same phase 

 of development, fused, these differences were invariably 

 equalized. In one case, however, where the change from 

 one generation of zooids to the next took place about four 

 days later in one colony than in the other, the equalization 

 was not accomplished before twenty days. This equaliza- 

 tion was repeatedly observed, and in most cases was accom- 

 plished much more quickly. Particular attention was not 

 devoted to sexual reproduction in fused colonies; but no 

 instance was noted in which one part of a fused colony 

 contained embryos while the other did not. Thus it is seen 

 that in physiological as well as morphological respects fused 

 colonies act exactly like a single colony. There is, how- 

 ever, one difference between the two. In the fused colonies 



