1 22 ALCYONIUM DIGITATUM. PAET m. 



carbonate of lime, for when Dr. Carpenter dissolved the 

 lime with dilute acid, a gelatinous substance remained, 

 which had the form of the spicules. Fig. 125 shows 

 those of the Alcyonium digitatum, or Dead Man's Fin- 

 gers, generally assumed as the type of this numerous 

 order, which contains sixteen genera and many species, 

 differing much in form but connected by a similarity of 

 digitate structure. 



The Alcyonium digitatum, when torn from the rock to 

 which these animals are attached, shrinks into a cream- 

 coloured fleshy mass of somewhat solid texture, rough 

 and hard to the touch, and studded all over with hol- 

 low depressions or pits. When put into sea-water, 

 these lumps, from the size of a pea and upwards, expand, 

 become semi-transparent, and from each depression a 

 polype protrudes its beautifully symmetrical eight- 

 petalled blossom. Their tentacles are short, broad, and 

 prehensile ; and the slender pinnse, which fringe their 

 edges arching outwards, are seen with a high magnifying 

 power to be rough with prickly rings, discovered by Mr. 

 Gosse to be accumulations of thread-cells with their 

 darts. 



These Alcyons, when expanded, are about an inch- 

 and-a-half high and two-thirds of an inch thick, but 

 individuals are met with two or three times as large, 

 and much divided into blunt finger-like lobes. The 

 sarcode mass of these compound animals is channelled 

 like a sponge, by branching canals, the orifices of which 

 open into the stomachs of the polypes; and, by bringing 

 them into communication with each other, unite the 

 whole into one compound animal, which is maintained 

 by the food caught and digested by each individual 

 polype. Currents of sea-water mixed with the nutri- 

 tious juices are made to circulate through the branching 

 canals by the vibrations of cilia with which they are 

 lined; they flow round the stomachs of the polypes, 



