FREE-LIVING NEMATODES 



495 



46 (45) Pharynx not long and narrow 47 



47 (48) Striae not resolvable into rows of dots Cephalobus Bastian. 



Genus of numerous species, frequent about the higher plants, doubtless often at least " semi- 

 parasitic." Occasionally species in fresh water. Common in decaying vegetable matter. 

 Some species are parthenogenetic, others hermaphroditic. Found on the surface of insects. 



Cephalobus resembles Rhabditis, but may readily be distinguished by the form of the pharynx 

 and the nature of the male caudal armature. The pharynx of Cephalobus is almost never 

 cylindroid or prismoid as in Rhabditis. On the contrary it tends to taper more or less regularly 

 from the base of the lips backward. Though simple in form the pharynx is usually compounded 

 of two or three series of short cuticula elements separated from each other by transverse 

 breaks. In a considerable number of species the lips aro modified so as to bear more or less 

 complicated forward pointing cuticula appendages. 

 Such forms are intermediate between the typical 

 Cephalobi and other genera, such as Acrobeles and 

 Wilsonema. The males of the Cephalobi do not 

 possess a bursa, at most showing faint indications of 

 such a structure. Nevertheless the papillae or ribs 

 found accompanying the bursa in Rhabditis are present 

 in Cephalobus, though they sometimes are less numer- 

 ous than on typical Rhabdites. 



Not infrequently the ovary functions in the first 

 instance as a testis. Spermatocytes appear in the 

 young ovary even before an external sexual opening 

 exists. The developing spermatozoa descend the 

 oviduct and enter the uterus. Later the oocytes de- 

 velop and are fertilized by the spermatozoa previ- 

 ously produced in the same organ, at least this 

 happens in some instances, and hence is assumed to 

 happen in all. So far no differences have been dis- 

 covered between spermatozoa produced in this way 

 by these syngonadic females and those produced by 

 the rarely occurring males. It is therefore fair to as- 

 sume that the sperm cells so commonly produced 

 in this way are potent. As in Rhabditis the renette 

 often takes the form of two long slender lateral ducts 

 ending blindly near the anus. Some species may be 

 revived after remaining months or even years in a dry ' 

 condition. 



Representative species. 



Cephalobus sub-elongatus Cobb 1914. 



The thin, transparent, colorless layers of the naked 

 cuticula are traversed by about seven hundred plain, 

 transverse striae, resolvable with high powers without 

 very much difficulty. There are three rather distinct, 

 bluntly conoid lips, which are rounded in front; each 

 of them apparently has two inconspicuous innervated 

 papillae. The intestine is composed of cells of such a 

 size that probably only about two are required to build 

 a circumference. The nerve-ring surrounds the esoph- 

 agus obliquely, and is accompanied by nerve cells, of 

 which the greater number are behind the nerve-ring 

 and in front of the cardiac bulb. 



Habitat: Moss Bog, W. End of Douglas Lake, Mich. 



FIG. 798. Cephalobus sub-elongatus. 

 Lateral view of a female. 

 a, lips; b, pharynx; c, anterior portion of esophagus; 



d, posterior extremity of anterior portion of esophagus; 



e, nerve-ring; /, cardiac bulb; g, beginning of intestine; 

 h, one of the cells of the intestine; i, lumen of the 

 intestine; j, excretory pore; k, cardiac valve; /, re- 

 nette cell; m, flexure in single ovary; n, cuticula; o, 

 ovary; p, spermatozoon in uterus; q, vulva; r, nucleus in 

 ovum; s, body cavity; t, anus; , ripe ovum; v, unripe 

 ovum; w, oocyte; x, blind end of ovary; y, rectum; a, 

 terminus. (After Cobb.) 



