ZooL.— Vol. III.] BANCROFT— COMPOUND ASCIDIANS. 1 47 



exhibiting this difference. Although the colonies were of 

 many different colors, the variation was the same. It con- 

 sisted in an increase in the proportion of red pigment in the 

 more vigorously growing edge. The following differences 

 were observed: — 



Whitish and very light yellow colonies had a reddish 

 edge. 



Distinctly yellowish colonies had an orange edge. 



Brownish colonies had a reddish brown edcre. 



Bluish black colonies had a purple edge. 



An extreme case of this variation, from another lot of 

 colonies, is shown in figs. 26 and 27, the last figure showing 

 the average condition on the edge and the first in the 

 center of the colony. In one of the colonies that was 

 watched most closely (represented by figs. 17-21) the 

 zooids on the growing edge had about the same general 

 tone as the rest of the colony, being usually yellowish, 

 though sometimes darker; but differed from the central 

 zooids in that the white dorsal double bands were more 

 feebly developed. Thus, at the time when figs. 20 and 

 21 from the growing edge were taken, the condition of the 

 double bands in the rest of the colony was about that rep- 

 resented in figs. 17 and 19. 



3. Variations Occurring at Different Times in the 

 Same Colony. 



(a) Due to Age. — Mature ova and young embryos are 

 salmon-colored (fig. 8), on account of the yolk they con- 

 tain; but as they grow older they become a very trans- 

 parent pink. When hatched, the larvae have the same 

 color, with a small amount of yellow and black pigment. 

 Young colonies with no more than a single system are still 

 more transparent. Their pigment is mostly confined to 

 endostyle and stomach. As they grow older, they become 

 pigmented on the surface, so that the internal organs do 

 not show through, but the colonies are still transparent 

 looking (figs. 9, 15). It is now that the color patterns can 



