492 



FRESH-WATER BIOLOGY 



36 (23) Esophagus plain Cryptonchus Cobb. 



Iff Y^^^y^^ PP Differs from Cylindrolaimns de Man in the form of the amphids, 



and the strongly developed esophagus with its various regions, in 

 the presence of a dorsal tooth at the base of the pharynx and in 

 the absence of setae. 



ccm 



Single species. 



Cryptonchus nudus Cobb 1913. 



H 



9 ...^..26; .'?.3'* ?.!.... ..> I 9 mm At a point about two 



" ^ ^^ '^ body widths in front of 



the cardia the nature of the esophagus suddenly changes, the 

 lining becoming notably less massive, and the radial structure 

 becoming relatively more massive, and at the same time changing 

 its character, so that there is a rather striking contrast between 

 this short posterior section and the main portion of the esophagus. 

 Wing space one-third as wide as the body. The anterior part of 

 the intestine for a distance equal to the body radius consists of 

 small cells packed wnth granules and possessing larger and differ- 

 ently formed nuclei. Eggs four times as long as the body is wide, 

 one-fourth as wide as long, and comparatively thick shelled; 

 uterus contains one at a time. 



Habitat: Found about the roots of aquatic plants, Potomac 

 River, Arhngton, and in Douglas Lake, Mich. 



Fig. 792. Cryptonchus nudus. lb, lip region; pp, labial papillae; am, 

 amphid; ph, pharynx; on, onchus or tooth; oe, esophagus; sp, spinneret. 

 XI81 '^^^^^^ Cobb.) 



Pharynx without teeth 38 



Esophagus with bulbs 39 



Amphids circular or nearly so ; pharynx compound, much elongated. 40 

 Cuticular external marking of amphid circular. . . Plectus Bastian. 



Genus of about thirty species mostly about plants. Some aquatic, none marine. Some 

 species, perhaps most, parthenogenetic or hermaphroditic. Obscure labial papillae usually present. 



Representative species Plectus tubifer Cobb 19 14. 



74 mm First lateral pore of the 

 cuticula immediately behind 

 the lateral organs, whence 

 79 mm. similar, somewhat smaller 

 pores, totaUing about two 

 hundred, form four subme- 

 dian rows. Six rounded, rather massive hps sur- 

 round the short, napiform vestibule leading to the 

 pharynx. Amphids transversely elongated or 

 roundish, open behind. There is an obscure, pos- 

 terior, more or less closed, elon- 

 gated, triquetrous pharyngeal 

 ^ J k 



sp 



37 (14) 



38 (49) 



39 (42) 



40 (41) 



XZ20 



Fig. 793- 

 a, mouth; 6, papilla-like cephalic setae; c, lateral organ; J, pharynx; e, posterior chamber of phar\'nx; 

 /, esophagus; g, nerve-ring; h, excretory pore; i, renette cell; j, glandular (?) cell; k, cardiac bulb; 

 /, cardia; m, intestine; n, blind end of anterior testicle; o, spermatocyte; p, flexure in posterior testicle; 

 q, blind end of posterior testicle; r, junction of testicles; s, vas deferens; /, glandular (?) organ; «, 

 muscle to one of the three supplementary organs; v, anterior supplementary organ; w, spiculum; x, anus; 

 y, one of the caudal papillae; 2, spinneret, (.\fter Cobb.) 



Plectus tubifer. Male, 

 lateral organ; J, pharynx; 



