428 H. BOSCHMA. 



however, gave a definite purplish blue color, proving that the 

 liquid contained amino-acids or peptids (cf. Howell, 1922). In 

 the tests the crab meat was practically unaltered, the liquid gave 

 only negative results with both reagents. 



THE FOOD OF ASTRANGIA AND THE SYMBIOTIC ALGJE. 



Among my material there were a great number of colonies the 

 polyps of which possessed numerous zooxanthellae in their ento- 

 derm. The feeding of these polyps therefore can to some extent 

 be compared with that of reef-corals, which, as a rule, also contain 

 large quantities of these unicellular algae. On the other hand the 

 polyps of Astrangia with the symbiotic organisms can be directly 

 compared with those of the same species which are completely 

 free of zooxanthellse. 



In the literature there are comperatively few notes on the food 

 of Madreporaria. According to the statements of many authors 

 (cf. Duerden, 1902; Gardiner, 1902-03; Pratt, 1906; Walther, 

 1919) only very rarely remnants of food are found in the gastric 

 cavity of madreporarian and also of alcyonarian polyps. Now 

 the greater part of the researches on which these statements are 

 based were made after the study of preserved material, and as I 

 have already pointed out before (Boschma, 1924) this is at least 

 partially due to the contraction of the polyps in the fixing fluid. 

 When coral-polyps strongly contract the food-remnants which 

 are in their gastric cavity usually are discharged through the 

 mouth. 4 In living coral-polyps from the reefs in the East Indian 

 region I usually found remnants of food in the gastric cavity 

 embedded in mucus. 



To ascertain the natural food of Astrangia I now proceeded in 

 the same way and studied the specimens in the living state. As 

 soon as the colonies were dredged I put them in sea-water on 

 board the ship and left them undisturbed for about a quarter of 

 an hour. Gradually the polyps now expanded more or less. 

 After a mechanical stimulus (a slight touch with a forceps) they 

 suddenly contracted, and at the same time the mouth opened 

 widely. Usually then at the bottom of the gastric cavity a slight 



4 Some years ago Dantan (1921) also tried to explain this lack of food in the 

 gastric cavity of anthozoans by the action of the preserving fluids which cause 

 contraction and emptying of the gastric cavity. 



