358 SYDNEY J. HICKSON. 



The degree to which the extensible portions of the polyps 

 contract on death is sometimes used as a character for the de- 

 termination of specific characters, but although it may be used 

 at times with advantage, it is one which should be used with 

 great caution. The group of spicules, which may be seen in 

 fig. 6 to extend from the surface of the colony a short distance 

 into the base of the extended portion, may be much more con- 

 siderable in some specimens than in others, and may aff'ord a 

 physical obstruction to the complete retraction of the polyps. 

 I have observed, too, that when a colony has remained in 

 imperfectly aerated water the polyps will die expanded, as sea- 

 anemones do; and a colony thus moribund when placed in 

 spirit will present a large number of expanded polyps. The 

 condition of the retraction of the polyps of a spirit specimen 

 of an Alcyonarian may depend, then, not only on anatomical 

 characters, but also on the condition of vitality, or want of it, 

 at the time the colony was preserved. These facts should not be 

 ignored, as they too frequently have been, in the determination 

 of species and the descriptions of new ones. 



Colour. — All the extended polyps of Alcyonium digita- 

 tum I have examined are perfectly white and transparent 

 when alive ; but in the specimens obtained in Provence the 

 spicules of the Halskrause (crown) are, according to Vogt and 

 Jung, sometimes reddish in colour. 



Tentacles. — The eight tentacles of Alcyonium digita- 

 tura are equal in size, and in the fully expanded condition 

 stand at right angles to the long axis of the polyps. They are 

 provided with a number of pinnae on each side, which varies 

 from twelve to twenty-two. 



It is not possible to count with accuracy the number of 

 pinnse in contracted or preserved specimens. Some of the 

 proximal pinnse are capable of being so completely withdrawn 

 that they are not visible except in the fully expanded condi- 

 tion. My numbers are given from the careful observation of 

 a great many fully expanded polyps in the Plymouth la- 

 boratory. 



In his description of the tentacles of A. palmatum, von 



