FREE-LIVING NEMATODES 



495 



47 



46 (45) Pharynx not long and narrow 



47 (48) Striae not resolvable into rows of dots Cephalohns Baslian. 



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



parasitic.' Occasionally species in fresh water. Common in deaiying veirctable maticr 

 Some species are parthenogenetic, others hermaphroditic. Found on iht- surface of iiw( t^ 



Cephalobus resembles Rhabditis, but may readily be distinguished by the form of the r,l,ir\nx 

 and the nature of the male caudal armature. The pharynx of Cephalobus is ahnosi m-v.-r 

 cyhndroid or prismoid as in Rhabditis. On the contrary it tends to tafK-r more or less reKularlv 

 from the base of the hps backward. Though simple in form the pharynx is usually comixjuiKled 

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

 breaks. In a considerable number of species the lips a.-j mjdiiied 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 Acrobelcs 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 bhndly near the anus. Some species may be 

 revived after remaining months or even years in a dry 

 condition. 



Representative species. 



Cephalobus suh-elongatus Cobb 19 14. 



^ 



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 recjuired to build 

 a circumference. The nerve-ring surrounds the esoph- 

 agus obhquely, 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, VV. End of Douglas Lake, Mich. 



_ Fig. 798. Cephalobus sub-elongatus. 

 Lateral view of a female. 

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



d, posterior extremity of anterior portion of esophagus; 



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

 //, one of the cells of the intestine; /, lumen of the 

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

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

 ovary; />, spermatozoon in uterus; q, vulva; r, nucleus in ^^^ 

 ovum; 5, body cavity; t, anus; u, ripe ovum; v, unripe 

 ovum; w, oocyte; x, blind end of ovary; y, rectum; 2, 

 terminus. (After Cobb.) 



