360 COELENTERATA ANTHOZOA chap. 



The zooids and coenenchym are usually protected by a crust 

 of coloured or colourless, long, smooth, needle -like, calcareous 

 spicules, situated principally in the superficial layer, so as to leave 

 the subjacent tissues soft and spongy in texture. In some cases 

 the spicules are smooth double clubs, rods, discs, or irregular 

 granules, and in Sarcophyllum, Chunella, some species of Umbellula 

 and others, there is no calcareous skeleton. The tuberculated 

 spindles, so common in other Alcyonaria, are not found in any 

 species. In most genera a horny, or calcified horny rod is 

 embedded in the central part of the axial polyp, serving as a 

 backbone or support for its muscles. It is absent, however, in 

 ^ Renilla, and reduced or absent in Cavernularia. 



The sexual organs are borne by the mesenteries of the auto- 

 zooids only, and each colony is either male or female. There is 

 no record of hermaphroditism in the order. The eggs contain 

 a considerable amount of yolk, and fertilisation is effected in the 

 sea-water after their discharge. The segmentation is irregular, 

 and the free-swimming ciliated larva (of Renilla) shows the 

 rudiments of the first buds from the axial polyp before it settles 

 down in the mud. 



The Sea-pens are usually found on muddy or sandy sea- 

 bottoms, from a depth of a few fathoms to the greatest depths of 

 the ocean. It is generally assumed that their normal position is 

 one with the peduncle embedded in the mud and the rachis erect. 

 Positive evidence of this was given by Eumphius, writing in 

 1741, in the case of Virgularia rumphii and V. juncea at 

 Amboina, 1 and by Darwin in the case of Stylatula darwinii at 

 Bahia Blanca. 2 



"At low water," writes Darwin, "hundreds of these zoophytes 

 might be seen projecting like stubble, with the truncate end 

 upwards, a few inches above the surface of the muddy sand. 

 When touched or pulled they suddenly drew themselves in with 

 force so as nearly or quite to disappear." 



It is not known whether the Pennatulids have the power of 

 moving from place to place when the local conditions become 

 unfavourable. It is quite probable that they have this power, 

 but the accounts given of the Sea-pens lying flat on the sand do 

 not appear to be founded on direct observation. The fable of 



1 Rumphius, Amboinsche Hariteitkamer, 1741, p. 64. 

 2 Darwin, Naturalist's Voyage round the World, 1845, p. 99. 



