^ESTIVATION OF BOTRYLLOIDES GASCOI DELLA VALLE. 163 



Botryllus, however, a long series of observations proved that there was such a senes- 

 cence, and that degeneration follows it. But here, as there was no process corre- 

 sponding to hibernation or aestivation, the colonies had no power of rejuvenescence 

 and died.* 



When the question is considered from the point of view of the amount of retard- 

 ation that occurs in normal budding, it is seen that the process in Botrylloides is 

 intermediate between that of the Polyclinidae and of Clavelina. For in the Poly- 

 clinidae the buds are formed normally and develop normally, but at a very slow rate. 

 In Botrylloides the buds are presumably formed normally, but do not develop 

 normally. While in Clavelina the buds are not formed at all until after the hiber- 

 nation is over. 



As regards the correspondence of the aestivating or hibernating processes with 

 the normal ones, Botrylloides as yet occupies a somewhat unique position, for, as has 

 been pointed out, a number of processes occurred here which have not yet been 

 observed in other colonies. Of the observations so far described as occurring in the 

 Botryllidae the only ones that are at all similar to those here described are some by 

 Pizon ('99, pp. 15, 25, 26, 37, 44). This author has described many cases of pre- 

 mature degeneration of buds and zooids, and has noticed that the zooids that tend 

 to degenerate are those which are more than usually separated from the majority 

 of zooids. It has already been seen that the premature degeneration of the buds 

 which were not near the growing edge was characteristic of the aestivating colony, 

 but even if this character is left out there are still the three following features: 



(1) The formation of a special lobe of the colony containing no zooids; 



(2) The separation of the buds from the parents at a very early stage, and their 

 removal to a distance from the zooids; and 



(3) The great irregularity in the appearance of the buds which makes it impos- 

 sible to say whether they belong to the same generation or not. 



All of these are phenomena which among the Botryllidae have hitherto only been 

 observed in this aestivating colony of Botrylloides gascoi. 



* In Botrylloides rubrum also there seems to be no such power, for Pizon, who has had the species under 

 observation for long periods, has not noticed anything of the kind. I, too, have kept the colony in unfa- 

 vorable conditions in an aquarium for long periods; and though it was more hardy than Botry'.lus, it became 

 considerably reduced in size, but still did not aestivate. 



