. The microscope and its revelations. lt;ln>n mil, vol. iii. 1870, p. -22 5. SPINES ; PEDICELLARI^E 889 and thus it would appear that the entire spine must be formed atonce, since no addition could be made either to its length or to itsdiameter, save on the outside of the sheath, where it is never to befound. The sheath itself often rises up in prominent points orridges on the surface of these spines ; but, as is shown in fig. 676,the reticular portion may have a share in the formation of the view of the mode of formation of the Cidarid spine is con-tested by Professor Jeffrey Be
. The microscope and its revelations. lt;ln>n mil, vol. iii. 1870, p. -22 5. SPINES ; PEDICELLARI^E 889 and thus it would appear that the entire spine must be formed atonce, since no addition could be made either to its length or to itsdiameter, save on the outside of the sheath, where it is never to befound. The sheath itself often rises up in prominent points orridges on the surface of these spines ; but, as is shown in fig. 676,the reticular portion may have a share in the formation of the view of the mode of formation of the Cidarid spine is con-tested by Professor Jeffrey Bell, who has brought forward x evidenceto show that if two spines of different sizes be taken from twoexamples of Cidaris metularia, also differing in size, the quantity ofsolid calcareous sheath seen in transverse section is proportionatelyless in the larger than in the smaller spine ; from this he concludesthat the growth is due to the internal reticulated portion ratherthan to the outer crust. The slender, almost filamentary spines. FIG. 677.—Spiue of Sputangus. of Spatanyus (fig. 677) and the innumerable minute hair-like pro-cesses attached to the shell of Clypeaster are composed of the likeregularly reticulated substance ; 2 and these are very beautiful objectsfor the lower powers of the microscope, when laid upon a blackground and examined by reflected light without any further prepara-tion. It is interesting also to find that the same structure presentsitself in the curious Pedicdlarice (forceps-like bodies often mounted onlong stalks), which are found on the surface of many Echinida andAsterida, and the nature of which was formerly a source of muchperplexity to naturalists, some having maintained that they wereparasites, whilst others considered them as proper appendages of theEchinus itself. The complete conformity which exists between thestructure of their skeleton and that of the animal to which they areattached removes all doubt of their being truly appendages to i
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