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



I. Variations of the Same Zooid. 



These are not particularly great in themselves, but as 

 one colony contains only adult zooids of one generation 

 at the same time, and as these all develop together, the 

 aggregate effect may be quite striking, and the general 

 appearance of the colony altered a good deal. Hence, in 

 comparing different colonies, or pieces of the same colony, 

 it is always necessary that the zooids be in the same phase. 

 Figures 5, 6 and 7 show the amount of variation that 

 normally occurs during the life of the same zooid. Often, 

 however, it is much greater. Figure 5, drawn when the 

 zooids were young and their parent generation had not 

 yet entirely degenerated, shows the extreme variation in 

 ground-color which a single zooid in this colony underwent. 

 Figures 6 and 7 are drawings of the two young zooids 

 represented in fig. 5, drawn respectively one and two days 

 later. They show to a small extent the elaboration of the 

 color pattern with increasing age. Where the color pattern 

 is more complex (as in fig. 10) this phenomenon can be 

 noticed much better. Then the young zooids present no 

 pattern at all, and it takes three or four days for the final 

 pattern to be evolved. 



2. Variations in Different Regions of the Same 



Colony. 



At Newport and Woods Hole nothing of this kind was 

 noticed. In all the colonies examined, all of the zooids 

 had exactly the same color. At Naples, however, the case 

 was different. Possibly the reason for this difference was 

 that at Naples a larger proportion of colonies were ex- 

 amined that were not in their prime. When describing the 

 habits of growth of the Naples colonies (p. 143), it was men- 

 tioned that the edges of the colony were often more 

 vigorous than the central parts. Accompanying this dif- 

 ference in vigor there is sometimes a difference in color. 

 Thus, in about -one hundred colonies twelve were found 



