34 88 



CCELENTERA TES 



In addition 

 to the small, is- 

 olated calcare- 

 ous particles 

 already men- 

 tioned within 

 the bodies of 

 the individual 

 polyps, sea- 

 pens have a 

 further support 

 in the form of a calcified and 

 often flexible axis, entirely 

 concealed in the stock and 

 pointed at the two ends. 

 The illustration on p. 3487 

 represents Pteroides spinosa, 

 in which the polyp-bearing 

 leaves are supported by a 

 number of calcareous rays 

 which project at the edges 

 as spines. 



The best known of the 

 sea-pens is the phosphores- 

 cent Pennatula phosphorea of 

 the Mediterranean and the 

 Atlantic. In this form the 

 capacity for giving light is 

 not possessed by the whole 

 surface of the stock, but 

 only by eight band-like or- 

 gans on the polyps them- 

 selves, the upper ends of which surround the mouth 

 like papillae, while their lower parts run down over the 

 stomach. These bands are filled with cells containing 

 fatty spherules, to which the phosphorescence is con- 

 fined. The fact that these luminous bodies have been 

 found in all parts of the stock is explained by the 

 liability of the bands to be injured, the least pressure 

 causing their contents to escape. Specimens which have 

 been roughly treated when captured and have strongly 

 contracted, as also those which have been kept for any 

 length of time in small vessels and have become dropsical, 

 are incapable of giving light. The phenomenon is only 

 observed in freshly-caught and little-disturbed animals. 



Umbellula thomsoni. 

 (Natural size.) 



Umbellula encrinus. 

 (Natural size.) 



