360 SYDNEY J. HICKSON. 



certain number of polyps in this condition by the chrom- 

 acetic acid method. 



Under the ordinary, somewhat unfavorable, conditions of life 

 in an aquarium the polyps do not usually expand more fully 

 than those represented in pi. xxxiv of Johnston's ' Zoophytes,' 

 the body-walls being fully extended, but the tentacle lightly 

 contracted, forming an eight-pointed star on the summit of 

 the polyp (PI. 37, fig. 9). 



The condition shown in fig. 10, in which there is no buUate 

 basal swelling to the tentacles, may be called the first stage of 

 contraction. 



The condition just described may be called the second stage 

 of contraction (fig. 9). 



In the third stage (fig. 7, 2') the tentacles become bent on 

 themselves, and a ring-shaped collar folds over the crown, 

 partially hiding it. 



In this condition the polyp contracts down to the level of 

 the surface of the colony. If they contract rapidly in response 

 to strong stimuli the body-wall is often very considerably dis- 

 tended; but if they contract slowly, either naturally or in con- 

 sequence of something distasteful in the water, they withdraw 

 below the surface of the colony without any alteration in their 

 diameter. 



When the crown has withdrawn below the surface of the 

 colony the basal portion of the body-wall of the extensible 

 portion of the polyp closes over the hole, the stomodseura 

 becomes folded like a concertina (fig. 7,4', St.), and the tentacles 

 become tightly drawn down. 



In the last stage of contraction (fig. 7, 5') the transparent 

 basal portion of the extensible portion of the polyp is drawn 

 down below the surface, and the aperture is tightly closed by 

 the opaque and densely spiculated crust of the colony, and at 

 the same time the tentacles, disc, and stomodajum become so 

 tightly pressed together that it is difficult in sections to make 

 out their outlines. 



Each tentacle is, when fully expanded, provided with a wide 

 lumen, as in all Alcyonaria. This lumen, which is a prolonga- 



