Report on the scientific results of the voyage of Challenger during the years 1873-76 : under the command of Captain George S Nares, , and Captain Frank Turle Thomson, . nd marginalia. Basalia.—The basalia are prominent spicules at the lower end of the Sponge,grouped together like bunches of long hairs, and forming the root-tuft which serves foranchoring the animal in the mud. This is one of the characteristic family peculiarities ofthe Hyalonematidse, but it also occurs in many Euplectellidse and some Rossellidfe. When the knowledge of the Hexactinellida was still limited
Report on the scientific results of the voyage of Challenger during the years 1873-76 : under the command of Captain George S Nares, , and Captain Frank Turle Thomson, . nd marginalia. Basalia.—The basalia are prominent spicules at the lower end of the Sponge,grouped together like bunches of long hairs, and forming the root-tuft which serves foranchoring the animal in the mud. This is one of the characteristic family peculiarities ofthe Hyalonematidse, but it also occurs in many Euplectellidse and some Rossellidfe. When the knowledge of the Hexactinellida was still limited to a few forms, such asEuplectella aspergiUum, Hyalonema sieholdii, and some Dictyonina, it was proposed toutilise the presence or absence of a root-tuft as a leading principle of classification, andto erect a special group of LophospongiaB. In this, the importance of what is merelyan adaption to the nature of the ground, was over estimated. We now know, in fact, REPORT ON THE HEXACTINELLIDA. 41 very closely related forms, perhaps even referable to the same genus, one of which occurson soft ground, and possesses a completely developed root-tuft, while the other, which Fig. 2.—Diagram of the arrangement of the Spicules. grows on a firm substratum, exhibits no trace of such a structure. It is, indeed, readilyconceivable that one and the same species might, in different circumstances, produce aroot-tuft or not. (ZOOL. CHALL. EXP.—PART LIU.—188G.) Ggg6 *2 THE VOYAGE OF CHALLENGER. The elongated spicules wliich form the root-tuft are either smooth or beset withbarbs, disposed iu various ways. While the upper end, which is concealed in theparenchyma, always runs out to a simple point, the free inferior extremity usually bearsan anchor-like structure, w^hich varies greatly in form and morphological significance. Aknob-like terminal swelling may occur, from the sides of which a few prongs, arrangedin a whorl, project obliquely upwards and outwards ; or aga
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectscienti, bookyear1887
