. Fresh-water biology. Freshwater biology. 466 FRESH-WATER BIOLOGY for instance, in the case of the supplementary organs of the males. These papillae, hairs, and setae all belong to the same general class of structures, but various terms are applied to them in accordance with their size and location. The special hairs found on and near the lips are known as cephalic setae, in contradistinction to the large hairs or setae sometimes found at the posterior extremity, the caudal and terminal setae. The setae are no doubt mainly tac- tile in function, though it seems certain that some of the ce- ph
. Fresh-water biology. Freshwater biology. 466 FRESH-WATER BIOLOGY for instance, in the case of the supplementary organs of the males. These papillae, hairs, and setae all belong to the same general class of structures, but various terms are applied to them in accordance with their size and location. The special hairs found on and near the lips are known as cephalic setae, in contradistinction to the large hairs or setae sometimes found at the posterior extremity, the caudal and terminal setae. The setae are no doubt mainly tac- tile in function, though it seems certain that some of the ce- phaHc setae and papillae serve 2 also as organs of taste and Fig. 768. Head of a nematode (diagrammatic), Smcll, view; 2, front view, showing triangular mouth opening in the middle. The ventral side to the right mi shows Xhc similar OrgaUS fouud OU the ampulla and excretory duct. As the right side of the o head is towards the spectator the lateral organ appears fVio rrt^n^ral cni-fa^oyrf +lio Kn/^-ir as a left-handed spiral. The arrangement of the cephalic ^'^^ general SUriaCe OI tUe DOQy setae is characteristic, the lateral ones being single, while ^ rpllprl Vipirc f\r cnmafir^ the submedian are in pairs whose members are of un- tl^C CallcU. IiaiFS Or SOmailC equ size. (A ter Co .) sctae. These probably follow a definite law in their distribution, but are so small that the exact distribution is difficult to make out and has been studied in but few cases. While it is not estabHshed that their distribution accords with a segmentation theory, this matter is worthy of care- ful study. Sometimes the hairs occur in harmonic repetition on successive groups of annules. The papillae of the cuticula are setae that do not project beyond the surface, or not far enough to entitle them to be called setae. They should not be confounded with pores, or with mere projections of the surface of the cuticula. Neither of these latter are innervated. Tactile structures sup- plementary to the se
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
