. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. PENNATULIDA. youngest polyps in each transverse series are those nearest to this Hne; the median hne and its more immediate surroundings is often also «steriles of polyps; when this is the case the naked streak, liow- ever, is narrower here than on the opposite surface, with the exception of the lower part towards the peduncle [Rciiilla, liowever, is a remark- able exception). Thus the two median surfaces of the stem are gener- ally easily distinguished '). Making the median line our star
. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. PENNATULIDA. youngest polyps in each transverse series are those nearest to this Hne; the median hne and its more immediate surroundings is often also «steriles of polyps; when this is the case the naked streak, liow- ever, is narrower here than on the opposite surface, with the exception of the lower part towards the peduncle [Rciiilla, liowever, is a remark- able exception). Thus the two median surfaces of the stem are gener- ally easily distinguished '). Making the median line our starting-point we might say that the surface D shows a centrifugal â development of the polyps, the surface V a -centripetalâ¢> one; so far we might well abandon the terms ventral and dorsal side, and instead of them use centrifugal and centripetal side; these latter names, however, are somewhat clumsy in descriptions, as is also the case, I think, with the terms proposed by Bourne-): prorhachis (for D) and metarhachis (for V)\ dorsal and ventral side are, and will always be, the most handy names, if only a rational choice were agreed upon. In my choice I have started from the following consideration; the stem of the sea-pens, rhachis -|- peduncle, is the direct product of the individual developed from the eg^ (the «oozooite of Lacaze Duthiers); this primary individual is for some time a solitary polyp of the typical octocorallian structure; accordingly, it is bilaterally symmetrical with respect to a plane naturally called a dorso-ventral plane; the mouth and pharynx (stomodaeum) are oval with the longer axis in the plane of symmetry; this plane bisects two median chambers, mutually diffe- rent and differing from all the others: only one of them contains re- tractor muscles, and this one is on the same side as the ciliated groove (sulcus, siphonoglyphe3)) of the pharynx; it has long ago been agreed on calling this «suicar side the ventral side in all polyps of octo-
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Keywords: ., bookcentury1800, bookdecade1890, booksu, booksubjectarcticregions
