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



be made out for the first time. A little later sexual repro- 

 duction begins, and the colonies may be said to be adult. 

 Most of the figures are taken from adult colonies. As old 

 age comes on, the pigmentation becomes progressively 

 deeper, and most of the color patterns again disappear. 

 Figure 16 shows the appearance of a colony that is about 

 to die. In its prime it looked more like the white-striped 

 zooids in fig. 23 (one of its offspring), having distinct 

 dorsal double bands and being much lighter colored. To 

 sum up, then: The older the colony the more deefly ;pig- 

 mented it is. Distinct color patterns are characteristic only 

 of colonies in their prime, being much less developed at both 

 ends of the series. 



(b) Due to External Influences. — The only external 

 influences that have been tested are unfavorable conditions, 

 such as exist in the aquaria, and in their natural environ- 

 ment when the competition of other organisms is too 

 strong. Figure 2 represents a system of a colony that had 

 been kept in a small aquarium with running water for 

 seventeen days. Other pieces of the same colony that 

 had been kept in the bay had the appearance of fig. 8, 

 except that the thin white coating on the posterior half of 

 the zooids was lacking. A piece of another related colony, 

 which, before being put in the aquarium, had the appear- 

 ance of fig. I, except that the cloacae were colored black, 

 underwent the same change. After fifty-nine days in the 

 aquarium it had exactly the appearance of fig. 2. When 

 removed from the aquarium and put back in the bay, 

 pieces of these colonies that had assumed the red color 

 sometimes regained their former vigor, and with it their 

 former color. When they did not do this they soon died. 

 Figures 11 and 12 represent another case. They are both 

 from the same colony, fig. 11 representing the colony in its 

 prime, and fig. 12 after it had been badly overgrown by 

 hydroids and was in rather poor condition. 



Besides changes like those mentioned, there are many 

 others whose cause cannot be so definitely made out. 



