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



single generation of zooids of the mother colony (Family I, 

 figs. 1-15; Family II, figs. 16-23; Family III, figs. 24-25.) 

 The methods employed have already been described on 

 page 139. Of these three families the first comprised at the 

 outset ninety-two colonies, of which thirty lived to develop 

 their mature color patterns. The second family started 

 with two hundred and sixteen colonies, and of these seven 

 lived to have their colors recorded. The third family 

 began with four colonies, of which two reached color 

 maturity. Most of the colonies that lived to develop thdir 

 mature color patterns were under continuous observation 

 for several months; the longest-lived of them for nearly 

 seven months. 



The color variation will be discussed in two sections: 

 first, the general character of the color variations observed 

 will be described; and second, the data thus obtained 

 applied to the consideration of the characters which may 

 safely be used to separate the described species of 

 Botryllus. 



- A. Nature of the Color Variation. 



As has long been known, the colors of Botryllus are due 

 to the many colored pigment-cells which it contains. In 

 general, each colony contains cells of three colors: first, 

 light colored cells, either white, light yellow, light green, or 

 yellowish green; second, dark colored cells, black, brown, 

 or deep blue; third, yellow, red, or orange cells. In any 

 one colony the color of each of these three classes of cells 

 is usually quite constant at any particular time. Thus, no 

 colony ordinarily has white and light green, or brown and 

 blue cells, but the variations present are caused by differ- 

 ent dispositions of cells of comparatively constant colors. 

 During the life of the same colony, however, and also in 

 succeeding generations of colonies, the color of each of 

 these three classes may vary considerably. Reference to 

 the figures will show what variations these three colors 

 underwent, and how they were combined in the three 

 families studied. 



