56 MICROSCOPICAL STUDIES. 



STUDY X. TYPICAL ALCYONARIA. 



The general characters of the central or typical form of these 

 colonial Anthozoa, have already been dealt with in outline in the 

 preceding note, and it therefore only remains to fill in some details. 



Two species of Alcyonium are found comparatively plentiful in 

 European seas ; the one, A. digitatum, stout and massive, with few 

 or no branches ; the other, A. palmatum, slender, arborescent, and 

 with fewer, but larger polyps. Normally the colonies of both species 

 are found attached by an extended base, but instances are known 

 where A. digitatum occurs in free, ball-like masses. 



The latter species is usually snowy white, but occasional pale 

 orange coloured varieties are found, the tint being due to the dif- 

 fusion of colour throughout the cellular tissue. A. palmatum on 

 the other hand, has very frequently a well marked variegated rosy 

 hue, extremely pretty and not affected at all by the extractive action 

 of alcohol. Curiously this is due to certain of the superficial spicules 

 containing iron oxide. The bright red tints of the fiery Pennatula 

 (Sea-pen) are due to a similar cause, and more important still, to 

 this is also due, the colour that gives commercial value and beauty 

 to red coral. 



In many ways these spicules are of great interest. Their shape 

 and arrangement, in conjunction with the form of the colony, furnish 

 the principal guides to the classification of the group. In A. pal- 

 matum there are five principal forms : (a) those of ruddy hue and 

 the largest in size (TOO -in. long), are arranged in eight bundles at the 

 bases of the tentacles. The spicules in each of these bundles con- 

 verge from right and left, arid form a strong framework support for 

 the free extremity of the polyp. The shape of each spicule is that 

 of a stout bent rod, tapering abruptly to a rough point at either end ; 

 warted too, but much less prominently than any of the others to be 

 mentioned. The foregoing pass at the apex of each bundle into 

 those (b) that act as the supporting skeleton of the tentacles. Their 

 general shape is rather more irregular, they are colourless, shorter, 

 and the warting is much stronger. Size 5 oo-in. (c) A dense irre- 

 gularly disposed layer crusting the general surface of the colony, 

 consists of small, strong-spiked straight rods .vSo-in. long. Most 

 peculiar forms are sometimes assumed, due to the great and irregular 

 development of the spines ; being sometimes broadly bilobed, some- 

 times even trifid. (e) In the interior of the colony, in the stiff 

 mesoglaea that divides and yet joins the different polyps, scattered 

 spicules, very slightly spined, and nearly straight, occur; while a 

 fifth form of spicule (d) occurs in the thick wall of the oesophagus. 

 These last are the smallest of any in the colony and barely measure 

 6^0 -in. long. 



