6 SIDERASTREA RADIANS. 



seen thus pulled at from each extremity. A large piece of a mollusc might 

 also be seized upon and partly ingested by two polyps at the same time, and 

 in the end their lips would approach and come into actual contact. A larval 

 polyp only four weeks old was able to hold a wriggling fragment of a small 

 worm and attempted to swallow it.* 



For examination of their anatomy and histology some of the polyps were 

 preserved in the partly expanded condition in 5 per cent, forrnol and others in 

 a solution of corrosive acetic, after narcotization with menthol or magnesium 

 sulphate. Shortly after preservation they were transferred to alcohol. Where 

 decalcification was necessary this was carried out by means of weak solutions 

 of hydrochloric or nitric acid, a few drops being added from time to time to 

 maintain a slight effervescence. For such a dense corallum as that of Sider- 

 astrea the process of decalcification required three or four days. After the 

 process the space heretofore filled by the skeleton was invariably found to 

 be occupied by a fluffy mass, which on examination under the microscope 

 was found to consist of delicate algal filaments along with fine organic 

 particles. Microscopic sections of the corallum were made by embedding in 

 Canada balsam and then grinding to sufficient thinness, as in the preparation 

 of ordinary rock sections. 



* Experiments conducted since this account was sent to the printerdemonstrate that the mucus exuded 

 by the ectoderm cells plays an important part in the feeding of coral polyps, particularly where the food 

 particles are small. The latter falling on the poljpal surface become embedded in mucus, and if not revers- 

 ing the ordinary direction of movement of the stomodaeal cilia they are slowly wafted away beyond the 

 tentacles ; nutritive particles and solutions bring about a reversal of the action of the stomodjeal cilia, and, 

 along with mucus in the form of strands or threads, are gradually drawn into the polypal cavity. 



