ZooL.— Vol. III.] BANCROFT— COMPOUND ASCIDIANS. l8l 



Furthermore, it is to be noted that by means of fusion 

 composite individuals may be formed which have all the 

 characteristics of the normal colony, except that the colors 

 of the zooids in the different parts of the composite colony 

 are usually different. 



It is seen that by the mere union of the two colonies to 

 form a single one, we obtain something more than the sum 

 of the two colonies. We obtain a single individual, — an 

 individual of a higher order, in which the metabolism and 

 reproduction of all the zooids is strictly coordinated in a 

 way which was not the case before fusion. 



VI. Appendix. 



Pizon (1900) has devoted considerable space to the 

 consideration of the phenomenon of the decrease in the 

 size of the ampullee and their pedicels, and its cause. 

 His principal conclusion is, "ces ampoules, d'abord tres 

 volumineuses et longuement pediculees dans les premiers 

 stades, diminuent progressivement pour prendre des dimen- 

 sions definitives beaucoup plus restreintes chez les colonies 

 un peu plus agees." The writer has seen this diminution 

 occurring much as described by Pizon, but only in the case 

 of colonies kept in aquaria. It is certain that this progres- 

 sive decrease in the size of the ampullce and their stalks 

 from the embryozooid through the next few generations 

 is not a process that takes place normally in a natural 

 environment, but is due to the unfavorable conditions in the 

 aquarium. There is no doubt that, even in their natural 

 habitat, the ampullae regularly decrease in size during the 

 resorption of the embryozooid, but the writer has noted 

 repeatedly that, soon after the first blastozooid opens its 

 siphons, the ampullse begin to grow larger again and to 

 extend out to the periphery of the test substance from 

 which they had been retracted. Before the first blastozooid 

 has begun to degenerate they are considerably larger and 

 much more numerous than they ever were during the life 



