FREE-LIVING NEMATODES 



493 



41 (40) Chitinous marking of amphid not circular. . . . Chronogaster Cobb. 



Genus closely related to Plectus, differing in much elongated cardia, connecting posterior 

 esophageal bulb and intestine. Ovary single in Chronogaster, double in Plectus. 



Single species known. . Chronogaster gracilis Cobb 1913. 



r.r/ 



JL 



2jT 



Male unknown. Habitat: Potomac 

 River; Douglas Lake, Michigan. 



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; o, flexure in 

 ovary; p, nucleus of ovum; q, blind end of ovary; 

 r, egg; s, vulva; t, anus; u, caudal gland; v, 

 spinneret. (After Cobb.) 



42(39) Amphids apparently absent; pharynx simple. . 

 43 (44) Esophagus with two bulbs; males with bursa. 



Rhabditis Dujardin. 



Genus of numerous species, some parasitic, especially in insects. 

 Several marine species and a number in fresh water. Common in 

 decaying matter. Reproduction 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 Rhabditis 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. Rhabditis cylindrica Cobb 1898. 



II. 



"IT/ 



J7_ 



u" 



55'" 



7.9" 



Habitat: Wet soils. 



FIG. 796. Rhabditis cylindrica Cobb. 



I, side view of female; II, side view of attached male; in, ventral view 

 of male tail. 



a, proximal end of spiculum; b, lip; c, base of pharynx; d, right spiculum; 

 e, bursa; /, anus; g, median bulb; h, nerve-ring; i, excretory pore; ], cardiac 

 collum; k, intestine; /, one of the ribs of the bursa; m, egg containing 

 embryo; n, flexure in ovary; o, lips; p, pharynx; q, segmenting egg; 

 r, median bulb; s, vulva; t, intromitted spicula; u, ejaculatory duct; P, 

 testicle; w, blind end of testicle; x, blind end of reflexed ovary; y, intestine; 

 z, anus. (After Cobb.) 



