. Comparative studies on certain features of nematodes and their significance. Nematoda. 26 ILLINOIS BIOLOGICAL MONOGRAPHS [130 of the three lips of the primitive form into two parts (Text figs. A and B). Division, tho incomplete, of these six lips gives rise to twelve lipped forms such as Anaxonchium litorium Cobb; complete division, to twelve small lips as Iotodorus punctulatus Cobb, and perhaps to the twelve highly modified lips or labial setae in Pomponema mirabile Cobb. Division of lips would then indicate a more evolved nature than the three lipped condition. This fact seems to be well b
. Comparative studies on certain features of nematodes and their significance. Nematoda. 26 ILLINOIS BIOLOGICAL MONOGRAPHS [130 of the three lips of the primitive form into two parts (Text figs. A and B). Division, tho incomplete, of these six lips gives rise to twelve lipped forms such as Anaxonchium litorium Cobb; complete division, to twelve small lips as Iotodorus punctulatus Cobb, and perhaps to the twelve highly modified lips or labial setae in Pomponema mirabile Cobb. Division of lips would then indicate a more evolved nature than the three lipped condition. This fact seems to be well borne out because many lipped forms occur among genera which have rather elaborate pharynges (Mononchus), and which have specialized in other lines too, like choice of habitat, loss of structures, as caudal glands and of one gonad by suppression. The Mononchs are to a large extent land inhabiting predatory nematodes rather more ad- vanced in this last respect than their fresh and salt water relatives. The six lipped condition permits the oral aperture to open widely allowing the mononch greater certainty in seizing its prey and macerating it against the pharyngeal Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hetherington, Duncan Charteris, 1895-. [Urbana, University of Illinois]
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