484 THE MICROSCOPE. 



and the margin of the disc is furnished with a series 01 

 white or "bright blue specks, which some observers believe 

 to be rudimentary organs of vision ; but they are rather 

 to be regarded as sac-shaped prolongations of the outer 

 layer, A transverse section of the 

 body of the actinia exhibits two 

 concentric tubes, the outer being 

 constituted by the body-wall, and 

 the inner by the digestive sac. 

 The wide space which intervenes 

 between these tubes is divided by 

 a number of radiating partitions, or 

 "mesenteries," arriving at definite 

 intervals from the inner surface of 

 Fig. zw.-Actinia urn, seen the body wall. To the face of the 

 from above with its crown of mesenteries are attached the repro- 



tentacles fully expanded, , . -i i 



ductive organs, which occur na 



thickened bands of a reddish tint, at certain periods 

 filled with ova. The animal has the power of effecting 

 considerable alterations of form, as well as of locomo- 

 tion ; although if well supplied with food it attaches 

 itself so firmly as not to be removed without laceration 

 of its base. 



Allied to the family Actinias are those laminated, in- 

 verted pyramidal looking bodies, Fungia, commonly called 

 " Sea-mushrooms," often found in great variety. The 

 colour of the polypidom is white, of a flattened round 

 shape, made up of thin plates or scales, embedded in a 

 translucent jelly-like substance, and within which is a 

 large polype ; the foot-stalk, by means of which the 

 animal is attached to the rock whereon it lives, is of a 

 calcareous nature. Ellis says : " The more elevated folds 

 or plaits have borders like the denticulated edge of 

 needlework-lace. These are covered with innumerable 

 oblong vesicles, formed of a gelatinous substance, which 

 appear alive under water, and may be observed to move 

 like an insect. I have observed these radiating folds of 

 the animal, which secrete the lamellae, and which shrink 

 between them when the animal contracts itself on being 

 disturbed. They are constantly moving in tremulous un- 

 dulations ; but the vesicles appeared to me to be air- 



