A BURROWING ANEMONE. 47 



tiples of six, and with usually two siphonoglyphs. The Octactinia 

 on the contrary, are all but entirely colonial, growing usually in 

 masses of many hundreds of associated individuals ; the mesenteries 

 are some multiple of eight ; only one siphonoglyph is present, and 

 the longitudinal muscle ridges of all the mesenteries face towards it 

 (Fig, 5). For convenience, -I shall call these the colonial anemones, 

 in contrast to the true or simple ones. 



Let us now examine briefly the special points about the types 

 chosen in our plates to illustrate the characteristic features of these 

 two divisions. 



SipJionactinia (PeacJiia) triphytta (Gosse), which we use as 

 type of the true anemones, is in many ways remarkable. Its body 

 is cylindrical, tapering to the base, which unlike that of other 

 anemones, is not broadened into a flat attachment disc but is nar- 

 rowed to a blunt point, and still more remarkable, is perforated by 

 a small opening. Around the mouth are set twelve stout swollen 

 tentacles, beautifully marked with dashes and lines of chocolate as is 

 too, in rather more irregular manner, the whole surface of the body, 

 on a ground tint of very pale pinkish brown. A stranger to the 

 strange convergence of outward form wrought upon animals of dif- 

 ferent groups by similarity in environment and in habits, would 

 never guess the true relationship of these animals living in the shell- 

 sand gravel that here and there accumulates in patches along the 

 shores of the Channel Islands ; he would surely presume them to be 

 some queer coloured sea-cucumber some Holothurian not figured 

 by Forbes. 



In habit Siphonactinia burrows down several inches into the 

 sand when the tide goes down, cautiously ascending and spreading 

 its tentacles level with the surface as the sea returns. 



Fig. 1 shows what is seen in a transverse section close under the 

 mouth disc. Notice the single siphonoglyph (si) giving attachment 

 to the ventral pair of directive mesenteries. The mesoglaea forms 

 the central layer in all the threefold walls and mesenteries of the 

 body. In the section from which this is drawn, the mesoglaea has 

 absorbed most of the stain used and has become very conspicuous by 

 reason of its bright crimson and glassy appearance. Fig. 2 represents 

 a section below the level of the oasophagus, and shows the swollen 

 free edges or craspeda of the primary mesenteries, as well as a 

 swollen region (gg) the ovary some distance from the edge. 



Few anemones arc so useful to use for a due understanding of the 

 general anatomy of the class, and the pity is, that this species is becom- 

 ing extremely rare. The trouble connected with the commoner species, 



