500 FRESH-WATER BIOLOGY 



59 (58) Cavity small, amphids usually well developed. 



60 



60 (61) Form of cavity conoid, open in front; circular amphids considerably 

 behind it • Monhystera Bastian. 



A large, aquatic genus of which about one hundred species are known. Many marine. 

 Some found in soil. Many species feed upon diatoms. Probably no other nematode genus 

 is so widespread as Monhystera. In any collection from land or from fresh or salt water the 

 first specimen to come to view often proves to be a Monhystera. The species are very numer- 

 ous and the individuals surprisingly so. Brightly colored eye-spots are more common than in 

 any other fresh-water genus. 



Representative species Monhystera sentiens Cobb 1914. 



t=»,i 



The striae are more readily visible 

 toward the extremities, especially the 

 posterior extremity. The lips appear 

 to be three in number, and are longi- 

 tudinally striated or fluted. The 

 anterior portion of the intestine is 

 somewhat bulbous in form, and is 

 separated from the esophagus on 

 the one side and the true intestine on 

 the other, by a pair of constrictions. 

 This portion may perhaps be looked 

 upon as a strongly developed cardia. 

 The lateral fields vary in width in 

 different parts of the body. A httle 

 in front of the anus they are about 

 two-fifths as wide as the correspond- 

 ing portion of the body, and contain 

 rather numerous scattered nuclei of 

 such a size that about eight would be 

 required to reach across the field. 

 A Httle farther forward the field is 

 narrower. Anteriorly it is wider 

 again. The blind end of the anterior 

 testis is located a short distance behind 

 the nerve-ring, while the blind end of 

 the posterior testis is located about as 

 far in front of the anus as the ter- 

 minus is behind it. The testes are 

 broad and in some parts appear to 

 fill up the main portion of the body 

 cavity. 



Habitat: Sand bar off Plummer's 

 Island, Potomac River. 



Fig. 805. Monhystera sentiens. 



I, side view of a female; II, side view of head of the same; III, side view of posterior extremity of a 

 male. 



a, pharynx; b, submedian cephalic seta; c, lateral cephalic seta; d, spermatozoon; e, amphid; /, lining 

 of esophagus; g, esophagus; /;, subcephalic setae; i, lumen of intestine; j, nerve cells; k, nerve-ring; 

 /, striated lip region; m, left spiculum; n, cell-nucleus associated with amphid; _ o, blind end of 

 single ovary; pp, the three caudal glands; q, anal muscles; r, spinneret; s, beginningof intestine; t, anus; 

 u, one of the cells composing the intestine; v, vulva; w, egg, the spermatozoa "d" being outside of the egg 

 "w"; *, egg in synapsis; y, vaginal glands; 2, ovum. (After Cobb.) 



