The porifera and coelentera . e stunted or suppressed, and themesenteries are ill-developed, but the sulcus is unusually large,and is provided with specially long cilia. Such specialised zooidsare distinguished as siphonozooids, and their function is to drivecurrents of water through the complex canal systems of the coloniesto which they belong (see Fig. XII. 4). Many forms of Alcyonaria have siphonozooids in addition tothe ordinary zooids (sometimes called autozooids), and are there-fore dimorphic; but the character is of no systematic value, for 1. — A typical Alcyonarian zooid showing then^
The porifera and coelentera . e stunted or suppressed, and themesenteries are ill-developed, but the sulcus is unusually large,and is provided with specially long cilia. Such specialised zooidsare distinguished as siphonozooids, and their function is to drivecurrents of water through the complex canal systems of the coloniesto which they belong (see Fig. XII. 4). Many forms of Alcyonaria have siphonozooids in addition tothe ordinary zooids (sometimes called autozooids), and are there-fore dimorphic; but the character is of no systematic value, for 1. — A typical Alcyonarian zooid showing then^\\t pinnate tentacles, t; the two long asulcarmesenteries, jdi and the six shorter mesenteries,i;t-. (Original.) 2.—Spicules oi Alcyonium, digitaimn. THE ANTHOZOA we find dimorphism occurring in individual species of manyfamilies which in other respects are widely separated from oneanother. Only in one group, the Pennatulacea, is dimorphism ofconstant occurrence. Much attention has been paid to the skeleton of the Alcyon-. Fio. IV. 1.—Transverse section throngh Uie stomoclaeiim of Funiculxna q^iadrangvlarif. sc, sulcus. •-.—Transverse section of the same species below the level of the stoniodaeuni. scvx, sulcarmesenteries; asrnx, asulcar 3.—Longitudinal section of a tentacle of AXcyoninw, digitatum. ec, ectodenn with ectodemiicner\e plexus; mg, niesa};lo«*a ; eii, endodenn. 4.—Transverse section through a portion of a mesentery of i^/ri/oninm diijitatitm, showingthe large retractor muscle fibres borne on branched processes of the , and the delicateprotractor muscles on the opi>osite face of the mesentery. .5.—Transverse section through one of the sulcar mesenterial filaments of w4/i-i/oniMm rfiyi-tatum, showing the glan<l cells, ijr, and the Hagellat cells,/o. 6.—Transverse section through an asulcar filament of the same species, showing the ojiengroove lineil by elongate ciliattHl ectaienn cells. 7, 7a, ~l>, 7r, (/.—Myoep
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
