ZooL— Vol. III.] BANCROFT— COMPOUND ASCIDIANS. 139 



natural habitat, vigorous growth and sexual reproduction 

 were easily obtained. Many other animals attached them- 

 selves regularly to the slide; in fact, bryozoa, worms, 

 barnacles, and other ascidians often grew there so vigor- 

 ously that they had to be removed periodically to save the 

 Botrylliis. There is nothing more fascinating than to 

 watch the waxing and waning of these other species. The 

 rapidity and suddenness with which some forms appear 

 and disappear, sometimes without having been crowded 

 out by competition, is absolutely dramatic. This method 

 of setting out slides in the normal habitat of the animals 

 to be studied is much to be recommended, not only for 

 investigations similar to those here described, but also 

 for faunistic and etiological studies. 



In order to follow the development of the brother and 

 sister colonies produced by the same mother, a colony 

 containing larv^ that were nearly ready to hatch was 

 isolated in a dish, the sides of which were lined with 

 glass slides. When the larvae hatched, many of them 

 attached themselves to the slides, which were then removed 

 and marked with a diamond. A drawing was made of 

 each slide, natural size, showing the exact location of each 

 of the embryozooids, so that later on the slides could be 

 placed over the drawings and any embryozooids that had 

 subsequently attached themselves to the slides could be 

 discovered and removed. The slides were examined in 

 this way at intervals, and all the foreign colonies removed, 

 so that there could be no doubt concerning the ancestry of 

 any of the colonies. In this way the three families of 

 colonies, which furnished most of the material for the study 

 of color variation and fusion of colonies, were reared. 



II. Natural History. 



The enemies of Botryllus and Botrylloides are of two 

 kinds: First, the enemies proper that prey upon the 

 colonies and eat them; second, the competitors that have 

 need of the same surface to which to attach themselves 



(2) January 14, 1903. 



