1 62 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



resembles Botrylhis at Naples. In the main, even the same 

 color variations are met with ; but their relative commonness 

 differs somewhat in the three localities. Judging from the 

 results here given, it would seem to be perfectly possible, 

 starting with a small number of colonies of nearly the same 

 color, and. preserving their offspring, to raise in the course 

 of a few generations all of the color varieties found in any 

 locality. 



IV. Fusion of Colonies. 



By fusion is meant the complete union of two originally 

 separate individuals into a single individual, accomplished 

 by means of simple growth without any operative procedure. 

 It has frequently been called concrescence by French 

 writers; but, in view of the wide use of this term in 

 embryological literature, fusion appears to be a better word. 

 The process has often been mentioned in zoological and 

 botanical literature; but it is only rarely that adequate 

 proof of its occurrence has been offered. Thus, for the 

 Tunicates, although a comparatively extensive literature on 

 this subject has sprung up, it is only the last paper dealing 

 with it (Pizon, 1900) that has recorded an observation 

 which proves the fusion of colonies to be a fact. One 

 circumstance that has tended to obscure the subject has 

 been the lack of clear distinction between the fusion of 

 colonies derived from separate embryozooids and the 

 fusion of zooids in the same colony. The last question 

 does not concern us here; it is merely a drawing closer of 

 the bonds which have already succeeded in keeping the 

 zooids in organic connection so as to form a colony. The 

 fusion of colonies, however, is of deeper significance, as it 

 gives us some insight into the forces that determine compe- 

 tition between neighboring colonies, and the question of 

 individuality. 



The question of the fusion of ascidian colonies was first 

 raised by Gegenbaur (1862, p. 166), who believed it proba- 

 ble that in Diploso^na ( Didemnum) gelatinosum many 



