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ESTIVATION OF BOTRYLLOIDES GASCOI DELLA VALLE. 



Botryllus, Botrylloides rubrum, and Botrylloides gascoi pointed in the same direction 

 except in the case of this aestivating colony. 



Before discussing this question for the sestivating colony I shall give a brief 

 summary of Pizon's results, as they are the only quantitative observations that have 

 been published, and I shall compare with these some results of my own which were 

 obtained under somewhat different conditions. Pizon determined carefully the length 

 of the following periods : 



1. The period between the beginning of the degeneration of the old zooids, as 

 marked by the closing of their siphons, and the first opening of the siphons of the 

 nest generation. (During this period there are no functional zooids in the colony.) 



2. The period of the adult life of the zooids, measured by the time during which 

 the siphons are open. 



3. The period of degeneration, during which the old zooids, after the closure of 

 their siphons, gradually disappear. 



The lengths of these three periods in days are briefly expressed in the following 

 table : 



TABLE II. 



My observations on this subject are not nearly so detailed as those of Pizon, as 

 I did not give it special attention. My impression, however, of the changing from 

 one generation of zooids to the next in colonies of Botrylloides rubrum and B. gascoi 

 kept in aquaria was that it took place about as slowly as described by Pizon, or per- 

 haps a little more rapidly. But the colonies of Botryllus that I studied were growing 

 on glass slides which were kept fastened to the lower side of a board floating in the 

 harbor near where Botryllus was growing naturally. In this way a perfectly natural 

 and very favorable environment was obtained, and it was noted that the length of 

 Period 2, the adult life of the zooid, was about the same as that observed by Pizon, 

 but Period 1 and Period 3 were very much shorter, lasting usually less than one day. 

 So rapid was the change of generations that, when observations were made only once 

 a day, considerable care was necessary to make sure that there had been any such 

 change. On one day there would be adult zooids with small buds, and on the next 



