I. INTRODUCTION. 



Although numerous observations have been published describing a partial dying 

 down of ascidian colonies during certain seasons of the year, nothing of this kind, so 

 far as I know, has as yet been described for any member of the Botryllidae. At 

 Naples, however, during the summer of 1899 it was my good fortune to have the 

 opportunity of observing such an occurrence in the case of Botrylloides gascoi.* 



The colony in question had been received from Dr. Lo Bianco on March 24. 

 It was cut in pieces, and these tied to slides which were set out in the bay where 

 the environment was perfectly normal. These were left undisturbed with only an 

 occasional examination until April 20, when one of the slides was removed to the 

 Zoological Station and kept in a small aquarium with running water. There it grew 

 well for a while, retaining the coloration normal for this species, but was not quite so 

 vigorous as the parts of the colony that were kept in the bay. This loss of vigor was 

 manifested by an increase in the time required to change from one generation of 

 zooids to the next. 



On June 29, however, a decided change was observed. At one end of the colony 

 a large lobe had grown out, which, so far as could be seen in the living colony, con- 

 tained nothing but ampullae, no zooids nor buds. This lobe did not have the blue 

 and red color of the species, but was a bright lemon-yellow, f The other part of the 

 colony had also undergone a change. It was now lilac in color, about half as thick 

 as it had been, and all of the zooids had degenerated, leaving nothing that could be 

 distinguished from ampulla 3 , and nothing in which beating hearts could be seen. In 

 spite of this lack of zooids, however, the ampullae were keeping up a vigorous circu- 

 lation, which was most rapid near the yellow lobe. 



On July 10 the blood had stopped flowing in the lilac part, which was dead and 

 disintegrating. The yellow part, however, was still maintaining a vigorous circu- 

 lation. On July 15 buds had appeared in the yellow part of the colony. This had 



* I wish to express my thanks to Harvard University for the advantages of a Parker Fellowship which I 

 enjoyed, and to the Smithsonian Institution, whose table at the Naples Zoological Station was put at my dis- 

 posal while this investigation was under way. 



f This lobe had been noticed some time before, but no particular importance was attached to it. The changes 

 in the other part of the colony, however, were not noticed until the latter had reached the condition described for 

 June 29. I think that these changes could not have begun before June 22 or they would certainly have been 

 detected. 



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