DEPARTMENT OF MARINE) BIOLOGY. 



141 



Attempts are being made certainly to ifill this gap by rearing colonies from 

 the plannla stage. These experiments will be subsequently described. 



As the records for one or two years clearly show variation in growth-rate 

 for different colonies of the same species, a consideration of the factors ac- 

 celerating or retarding growth becomes necessary. At present it seems that 

 strong light and pure ocean-water are two accelerating factors, but the data 

 on them are vague. A thorough knowledge, which we do not now possess, 

 of the feeding-habits and the food-supply is essential before these problems 

 can be solved. 



The tiles planted on the reefs in 1909, in the hope that young corals would 

 settle on them and furnish material for growth observations, had collected 

 nothing in 1910, but were left undisturbed, hoping for ultimate success. 



REARING CORALS FROM PLANUL^. 



Results of previous attempts. — During the field season of 1908 planulse of 

 Favia fragum attached themselves to the bottom of a glass vessel, which was 

 placed in a live-car that broke its moorings during a storm. These planulae 

 attached themselves between May 11 and 18, 1908, and on July 22, when 

 measured by Dr. Mayer, had attained a size ranging from 3.5 X 4 mni. to 5 

 mm. in diameter. In 1909, twelve tiles bearing attached young were planted, 

 but in 1910 no trace of living coral could be found on them, all evidently 

 having died. 



Experiments in ipio. — In 1910, 50 cultures were made, as follows: 



Planula Cultures made in igio. 



The culture technique was considerably improved during this season and 

 will be briefly described. An effort is made to have the planulae settle on tiles 

 having a central perforation by which they may be fitted over the heads of 

 iron stakes. The tiles have a diameter of 8 inches and are placed in jars, 

 the inside diameter of which is about 8.25 inches and the depth about 8.5 

 inches. After the bottom of a jar has been covered with the cleanest sand 

 obtainable, a tile is placed in it and the central perforation and the space be- 

 tween the periphery of the tile and the sides of the jar are filled with sand 

 to the level of the upper surface of the tile. Filling these spaces is necessary, 

 as the planulse tend to settle in depressions. After this preparation, fresh 

 sea-water is gently poured in through a funnel until the jar is nearly full. 

 The extruded planulae are pipetted from the vessel containing the parent 

 colony and placed in the culture-jar prepared for their reception. 



To get the best results, the water in the culture-jar should be changed at 

 least once a day. This may be done by several devices. In order not to draw 



