. The Cambridge natural history. Zoology. 14 HEMICHORDATA ,. of the dorsal body-wall, a conspicuous external feature of the species in which they are present. The most interesting- peculiarity of the digestive tract in this region is the existence, in certain species, of pores, possibly vestigial gill- slits, leading from it to the exterior. Notochord and Skeleton. —The structure compared by Bateson with the Vertebrate notochord is a hollow dorsal outgrowth of the alimentary canal of the collar-region (Fig. 7, n). Near its origin it is slender, but in the proboscis it dilates into a com
. The Cambridge natural history. Zoology. 14 HEMICHORDATA ,. of the dorsal body-wall, a conspicuous external feature of the species in which they are present. The most interesting- peculiarity of the digestive tract in this region is the existence, in certain species, of pores, possibly vestigial gill- slits, leading from it to the exterior. Notochord and Skeleton. —The structure compared by Bateson with the Vertebrate notochord is a hollow dorsal outgrowth of the alimentary canal of the collar-region (Fig. 7, n). Near its origin it is slender, but in the proboscis it dilates into a comparatively large organ, which in most cases retains its cavity. Its cells have a vacuolated appear- ance, which recalls the fine structure of the Vertebrate notochord. In Schizocardium and Glaiidiceps, the organ is produced into a slender " ver- miform process" (;'), w^hich extends nearly to the tip of the proboscis. The main support of the. Fi(j. 7.—Schizocardium brasilienne ; longi- tudinal, median section through the pro- boscis, the collar, and the first part of the T^^obospis ^t'llk is " thp " i^rn trunk; h, main blood-space of tlie pro- prODOSClS-Staik IS tne pro- boscis ; \ h.(?, ^, first, second and boscis - skeleton " (s), a A- third body-cavities ; cm, circular muscles it i -i • of proboscis; e, epidermis; , longi- shaped Organ whose median tudinai muscles of proboscis; m, mouth ; part lies beneath the base of w, notochord ; , central nervous system, , i. \^ ^ u A' continuous witli the subepidermic nerve- tlie notOCUOrcl, itS diverging plexus (black) of tiie proboscis, and witii lecrg extending backwards the dorsal nerve [d) ; , pericardium ; , . , ^..9, proboscis-stalk; s, proboscis-skeh- along the outer Side ot the ton; ^vermiform process of notochord. alimentary canal of the collar. (After Spengel.) "^ The proboscis-skeleton, like the branchial skeleton, is a special development of the structure- less membrane whi
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
