138 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



I. Introduction. 



These investigations were carried on at Woods Hole 

 during the summer of 1898, and at Naples, from April 

 to November, inclusive, 1899. They were made possible 

 by an appointment to a Parker Fellowship in Harvard 

 University, for which the writer wishes to express his 

 thanks. Thanks are also due to the United States Fish 

 Commission for the advantages enjoyed at its laboratory 

 at Woods Hole, and especially to Professor H. C. Bumpus, 

 for the excellent opportunities for research afforded. Fur- 

 thermore, thanks are due the Smithsonian Institution and 

 the committee in charge of the University Table for the 

 use of their tables at the Naples Zoological Station. 

 Finally, it is the pleasant duty of the writer to record his 

 obligations to Geheimrath Dr. Dohrn and the staff of the 

 Zoological Station at Naples for the constant kindness with 

 which all his wishes were met. 



This paper is concerned only with the study of living 

 colonies of Botryllus and Botrylloides, both incrusting 

 compound ascidians. To facilitate the handling of the 

 animals and allow an examination of both upper and lower 

 surfaces, the colonies were reared attached to glass slides. 

 They were easily fastened to the slides by tying down 

 the edges, especially those containing the ampulla. In 

 vigorous colonies kept in their natural environment one or 

 two days sufficed for forming a firm attachment, when the 

 strings could be removed. When, however, the colonies 

 were kept in aquaria, the attachment took place more 

 slowly. 



It was found that colonies kept in aquaria » would not 

 do well. They would live for months and bud regularly, 

 but would not grow vigorously nor reproduce sexually. 

 Accordingly, the slides, with the colonies attached, were 

 fastened on the under side of a board that was kept 

 floating in the bay near where Botryllus was growing of 

 its own accord. By means of thus placing them in their 



