152 ESTIVATION OF BOTRYLLOIDES GASCOI DELLA VALLE. 



finally they developed again into zooids. They were probably carried into the yellow 

 lobe both by the general circulation, and by the growth of the vessels containing 

 them. Unfortunately, however, I have no observations on any of these points, for 

 at the time when the yellow lobe was developing I had no idea of its significance. 

 It is to be hoped that some future investigator will preserve and section the early 

 stages of the development of the yellow lobe before the degeneration of the rest of the 

 colony, and discover why in this case the buds separate from the parent zooids at 

 such an early stage. 



V. PERIOD OF REJUVENESCENCE. 



The life of the aestivating colony may be conveniently divided into two periods: 



1. The ^Estivation proper, June 29 to July 15, during which the colony contains 

 no functional zooids, that is, zooids with open siphons. During this period life is at 

 its lowest ebb, food comes exclusively from stored material, and the circulation is 

 kept up almost entirely by the contractions of the ampullae. In fact, during the 

 greater part of this period, after the hearts of the old zooids stop beating, and before 

 the hearts of the older buds begin, the ampullae alone maintain the circulation. 



2. The Rejuvenescence, July 15 to September 17, during which the colony 

 gradually assumes the condition normal to the species. This is the period which is 

 now to be discussed. 



The dates and main facts in the life of the colony are given in Table I, which 

 renders a detailed description unnecessary. 



We may now pass on to a few facts of interest in connection with the rejuven- 

 ating colony. 



i. Correlation between Growth and Vigor. — Here we see that, just as is the case 

 with colonies of Botryllus (Bancroft, :02),* vigor is always associated with growth. 

 The tendency was not towards a stationary condition. There was either advance 

 or retrogression. Thus the yellow lobe grew out and the rest of the colony degen- 

 erated and died. The yellow lobe became differentiated into an opaque part which 



* In the paper referred to it was shown that the normal condition of Botryllus at Naples is one of active 

 growth. When this stops, the colony degenerates and soon dies. Among the parts of each colony the same condi- 

 tions usually obtain. Thus the edge, and the new parts of the colony generally, are growing and vigorous; while 

 the centre or older parts are stationary or degenerating. Pizon ('99, pp. 39, 41) has described a similar case where 

 the zooids developed best at the edge of the colony and almost all the life became concentrated there, the circu- 

 lation near the centre having almost stopped. I think that the reason the zooids begin to do better at the 

 periphery of the colonies is that the great majority of the ampullae is located there. As the contractions of the 

 ampullae aid the circulation very materially, the zooids at the periphery will be nourished better, especially in 

 their younger stages, and thus be more vigorous. 



