164 ESTIVATION OF BOTRYLLOIDES GASCOI BELLA VALLE. 



VI. SUMMARY. 



1. In a colony of Botrylloides gascoi Delia Valle kept in an aquarium a yellow 

 lobe containing no zooids was developed. 



2. Later all the zooids degenerated, and finally all of the colony except the yellow 

 lobe died. 



3. The ampullae kept up a circulation in the isolated lobe for about two weeks, 

 after which buds reappeared in it. 



4. An examination of sections of half the colony showed that there were small 

 isolated buds, probably produced by the zooids which had degenerated, scattered all 

 through the colony. 



5. The colony gradually recovered its former condition except that it always 

 retained its yellow color which is characteristic of Botrylloides luteum v. Drasche. 

 Therefore this species is a seasonal variation of B. gascoi. 



6. During the rejuvenescence of the colony it differed from the normal colony 

 in the following additional particulars : 



a. The intervals between generations of adult zooids were longer. 



b. Buds were liable to appear at any time and at any place in the colony, and to 

 degenerate at any time, so that frequently regular generations could not be distin- 

 guished. 



c. A certain part of the colony, the growing edge, was constantly wandering 

 about occupying a new substratum. In this part most of the buds appeared. They 

 accompanied it in the wanderings and moved so that their branchial ends were always 

 directed forwards. Consequently aggregations of good-sized buds were seen which 

 were not grouped into systems. 



7. The cause of these deviations from the norm seems to be the inadequacy of 

 the food-supply. This was not enough for the whole colony and so the most vigorous 

 part, whose ampullae maintained the best circulation, got most of the food. Conse- 

 quently the buds situated in this region got more food and developed more rapidly 

 than those of other regions. 



8. This case of aestivation is in general similar to the hibernation described for 

 the ascidians. 



