. The microscope and its revelations. eautiful structure is better made out whenthe animal membrane that incloses it has been got rid of by boilingin a solution of caustic potass; and the appearance of one of thefive segments of which it is composed, when thus prepared, is shownin fig. 674. The most beautiful display of this reticulated structure, however,is shown in the conformation of the spines of Echinus, Cidfiris, &c.,in which it is combined with solid ribs or pillars, disposed in such amanner as to increase the strength of these organs, a, regular andelaborate pattern being formed by the
. The microscope and its revelations. eautiful structure is better made out whenthe animal membrane that incloses it has been got rid of by boilingin a solution of caustic potass; and the appearance of one of thefive segments of which it is composed, when thus prepared, is shownin fig. 674. The most beautiful display of this reticulated structure, however,is shown in the conformation of the spines of Echinus, Cidfiris, &c.,in which it is combined with solid ribs or pillars, disposed in such amanner as to increase the strength of these organs, a, regular andelaborate pattern being formed by their intermixture, which showsconsiderable variety in different species. When we make a thintransverse section of almost any spine belonging to the genusEchinus (the small spines of our British species, however, beingexceptional in this respect) or its immediate allies, we see it to be 386 ECHIXODEIOIA made up of a number of concentric layers, arranged in a manner thatstrongly reminds us of the concentric lings of an exogenous tree. FK;. C7i5.—Transverse section of spine of Echinometra. (fig. 673). The number of these layers is extremely variable, de-pending not merely upon the age of the spine, but (as will presently appear) upon the part ofits length from which thesection happens to betaken. The centre isusually occupied by avery open network (fig.(572) ; and this is boundedby a row of transparentspaces (like those at a «,b b. r c, &c., fig, ).which on a cursory in-fection might be sup-posed to lie \ did, but are Ki,.. (J74.— On, o\ bhe segments of the calcareous found on closer exnmina-skeleton of an ambulacral disc of
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
