ZooL.— Vol. III.] BANCROFT— COMPOUND ASCIDIANS. 149 



They are probably dependent upon changes in the vigor of 

 the colonies due to age and environment. In fact, with few 

 exceptions, all the colonies were constantly changing their 

 colors. Thus, at one time, the colony represented by 

 figs. 17 to 21 was in many pieces, distributed upon a 

 number of slides. Although they had all been fastened to 

 the same board, where the environment should be com- 

 paratively constant, the different pieces hardly ever had 

 the same appearance. Thus, on one day the ground-color 

 varied from transparent gray to dull black, and to dark 

 brown, with all gradations in between. The double 

 bands were present in all cases, and of medium thickness. 

 To show the character of some of the changes, part of 

 the records for one colony is here given. 



August I. (Fig. 8.) There is a good deal of varia- 

 tion in the colony, due to differences in the thickness of 

 the coating of light-colored pigment, so that sometimes 

 the zooids have their anterior half dark and their posterior 

 half light colored; sometimes they are streaked longi- 

 tudinally with black and white; and sometimes they are 

 almost entirely black near the cloaca, white in the middle, 

 and brownish yellow at the anterior end. 



August 18. Piece I. — In good condition. Figure 8 still 

 represents a good average zooid. 



Piece II (on another slide). — The colony is growing, but 

 not very well. The color is intermediate between figs. 

 I and 8, nearest 8; but some of the zooids have no white 

 coating at all, only irregular markings and a few sparse, 

 isolated dots. A few zooids have a well developed coating. 



September 2. Piece I. — Color darker than fig. 8. The 

 coating is a decided lemon yellow. 



September 8. Piece I. — One end of the colony with 

 younger zooids has very distinct yellow coatings, while 

 at the other end the older zooids, which have buds nearly 

 ready to replace them, are streaked and without any dis- 

 tinct coating. 



