. Fresh-water biology. Freshwater biology. i 2 3' 2-6 3 1 6 2 12 25. -M-** 92 7 9 ij (.-^l.» Male unknown. Habitat: Potomac River; Douglas Lake, Figs. 794 and 795. Chronogaster gracilis, a, lips; b, papilla; c, cephalic seta; d, pharynx; e, esophagus; /, posterior chamber of pharynx; g, problematical organs; h, nerve-ring; i, excretory pore; j, renette cell; /, valvular apparatus in cardiac bulb; m, cardia; n, intestine; 0, flexure in ovary; p, nucleus of ovum; g, blind end of ovary; r, egg; s, vulva; t, anus; «, caudal gland; v, "⢠'^» spinneret. (After Cobb.) 42
. Fresh-water biology. Freshwater biology. i 2 3' 2-6 3 1 6 2 12 25. -M-** 92 7 9 ij (.-^l.» Male unknown. Habitat: Potomac River; Douglas Lake, Figs. 794 and 795. Chronogaster gracilis, a, lips; b, papilla; c, cephalic seta; d, pharynx; e, esophagus; /, posterior chamber of pharynx; g, problematical organs; h, nerve-ring; i, excretory pore; j, renette cell; /, valvular apparatus in cardiac bulb; m, cardia; n, intestine; 0, flexure in ovary; p, nucleus of ovum; g, blind end of ovary; r, egg; s, vulva; t, anus; «, caudal gland; v, "⢠'^» spinneret. (After Cobb.) 42 (39) Amphids apparently absent; pharynx simple 43 43 (44) Esophagus with two bulbs; males with bursa. Rhahditis Dujardin. Genus of numerous species, some parasitic, especially in insects. Several marine species and, a number in fresh water. Common in decaying matter. Reproductioti wonderfully varied, ranging from parthenogenesis, through hermaphroditism of varying degree to com- plete bi-sexuality. Many species microbivorous. In some species there is a marked alternation of generations. Bursa better developed in species of Rhahditis than in any other fresh-water nematodes. Other genera presenting this feature are Tylenchus, Dolichodorus, and Oncholaimellus. Bursa (Fig. Ill) consists of two thin lateral extensions of cuticula containing rays or ribs, often tubular, constituting outlets of cement glands, always well supplied with nerve endings. Form of bursa and arrangement of its rays form good generic and specific characters. Representative species. Rhahditis cylindrica Cobb 1898. h i= Fig. 796. Rhahditis cylindrica Cobb. I, side view of female; II, side view of attached male; III, ventral view of male tail. a, proximal end of spiculura; h, lip; c, base of pharynx; d, right spiculum; e, bursa; /, anus; g, median bulb; h, nerve-ring; i, excretory pore; j, cardiac collum; k, intestine; /, one of the ribs of the bursa; m, egg containing embryo; », flexure in ovary; 0, l
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
