papillary airangenicnt as aid tiie writers (i'.i:i:<i. Since the 

 lips are not forinefl from the esophageal primordium but from 

 the cells of tlie anterior end (clavate cells of the papillary 

 nerves and arcade lobes) the esophagus has nothing to do with 

 them. The clavate cells are hexaradiately symmetrical while 

 the arcade is bilaterally symmetrical with a gross triradiate 

 and an actual 9-radiate symmetry (Fig. 4(36). Tlie actual 

 Sl-radiate symmetry is subdivisible into a triradiate and a 

 hexaradiate formation rather than into three triradiate sys- 

 tems. We shall assume a hexaradiate symmetry as basic. 

 Taking either extreme, six distinct lips or three distinct lips 

 one finds repetitive series of transitions from the one to the 

 other in the large groups. The lips themselves are subdivisible 

 into two portions, the apical part, bearing the internal circle 

 of papillae and the basal part, bearing the external circle of 

 jiapillae and amphids in the Phasmidia and at least one sub- 

 division of the external circle in the Aphasniidia. In some 

 instances the tw^o parts of a lip may be represented by sepa- 

 rate lobes as in Spironoura affine and Parascaris eqiiorinn 

 (Fig. 37) while in other instances, O-ri/iiris equi, Metonchn- 

 laimiis pristiunis (Figs. 57 and 63) only the a|iical lobes nmy 

 persist. 



Original lips may totally disappear and be replaced by newly 

 formed structures such as the pseudolabia of sjiiruroids, the 

 probolae of ceplialobids and the pseudonchia of filariids. 



In the study of cephalic structures the student should be 

 ([uite critical. It is not uncommon for two workers examining 

 the .same species to find greater differences than one worker 

 would find examining representatives of two families. Lateral 

 and medial views are often quite helpful but without an en 

 face view they may be meaningless. It is due to this fact 

 that the majoritj' of older descriptions of the cephalic struc- 

 tures of parasitic nemas must be considered valueless. In 

 examining en face views great care should be taken in focus 

 ing the microscope, and oil immersion is essential even in the 

 study of the largest species. 



A. PHASMIDIA 



Phasmidians are similar to one another in the possession of 

 simple external amphids, usually pore like and labial in posi- 

 tion. The cephalic .sensory organs are nearly always papilli- 

 form and in the most extreme cases are no more than setose 

 papillae. In cases of reduction or fusion of the external circle 

 it is always the dorsodorsals and ventroventrals that tend to 

 disappear. The physiognomy of the various members of the 

 subclass will be dealt with systematically. 



Ehabditina. Members of the suborder Rliabditina (Figs. 

 r)4-.5ri) characteristically have six lips but three lipped forms 

 are C|uite common and many genera have no lips. The cephalic 

 papillary arrangement is likewise diverse. 



Rhabditidae. — Both six and three-lipped forms are common 

 in the Rhabditidae and one finds every conceivable variation 

 between the two. In SliahiJitis terricota there are six large 

 separate lips, an internal circle of six well developed papillae 

 and an external circle of ten well developed papillae ; the latter 

 are not absolutely equal in form or size, the dorsodorsals and 

 ventroventrals being similar as are the laterodor.sals and latero 

 ventrals while the ventrolaterals are more or less intermediate 

 between the others. Bhabditis liicanii has three basally bilobed 

 lips and the same number and aiiangement of papillae but in 

 this instance the ventrolaterals are small and like the dorso 

 dor.sals and ventroventrals. Other rhabditids vary between 

 these types some having di.screte, some confluent lips; in some 

 the labial region is set off from the remainder of the bod.v 

 while in others tliis is not tlie case. In all instances the am- 

 phids are dorsolateral and laliial in position and pore-like in 

 character. 



In Diploscaptcr curonafa the lips have been entirely trans- 

 formed into a pair of medial, outwardly acting, distally bifur- 

 cate fossores and a pair of lateral lamellae. Neither papillae 

 nor amphids have been satisfactorily studied. 



C^yliniirogasterids have six discrete lips which may or ma.y 

 not be set off from the remainder of the body; there is an 

 internal circle of six reduced pajiillae. In Lonf/ibncca rivipara 

 and /,. lasiiira there is an external circle of four well develojH'd 

 li.'jpillae (laterodoi'sals and lateroventrals) and in the latter 

 veiitrcdaterals are also present but reduced. In Ci/linilraf/nxtrr 

 lonz/istoma there arc six well developed (Id., vd., and Iv.) and 

 four reduced (dd. and vv.) pai>illae. The amphids are dorso- 

 lateral and labial in all forms. 



In the family Diplogasteridac the two chief groui)s b.-i.sed 

 upon the eso])hagus, Alloioncmatinae and Diplogasterinae, 

 seem to differ also in cephalic characters. Members of the 

 Alloioncmatinae usually have rather distinct lips, six (.11 

 loioncma appcnilioiilatum. v. iliibium) or four (Clicilobim qua 

 <lril<il)ia1ii.'.) ; in the latter instance the submedial lips .are 



fused : only six papillae have been observed, these presumably 

 being the laterodorsal, lateroventral and ventrolaterals. Al- 

 loionematids have pore like, labial, dorsolateral amphids and 

 a simple hexagonal oral opening. The clo.sely related family 

 Strongyloididae is characterized by two lateral lips, this being 

 practically the only character distinguishing the free-living 

 generation from such genera as AUoionrma and Rhabdito- 

 phancs. Diplogasterids usually have no lips (Diplogaslir 

 flctur, Mononclwides ainericanus (Syn. Diplogaster americanus) ) 

 but instead they have a thin circum-oral membrane supported 

 by longitudinal rugae which project anteriorly from the stoma. 

 The number and degree of development of the rugae differs 

 in the various species. In other genera inconspicuous rem- 

 nants of six lips may be present ( Prist iiiin-lnis, Rliabditidaidrs, 

 Odonlopharjini') . Among the forms thus far studied, Pris 

 tionclius acrivora is the only one known to show the full com- 

 ponent of papillae (16) ; in this instance the dorsodorsal and 

 ventroventral papillae are reduced while the others are well 

 developed. In all other members of this subfamily studied the 

 internal circle and the externomedial papillae are rudimentary 

 or apparently absent. The remaining six papillae are often 

 conically setose. Another peculiarity of the group is that the 

 amphids vary from pore like and labial in position to slit or 

 transvensely elliptical (with similarities to PIcctiis). 



The family Cephalobidae contains forms with six lips (Paiia- 

 grolaimiis siibclotinatiis), three lips (Ccphalobiis pcrsegnis, 

 Trici'iihalobus longicaudatiis) three simple (Acrobeloides 

 Ijiitschlii) or bifid labial probolae and sometimes six cephalic 

 probolae (Acrnbelcs coinplexus). Labial probolae are cuticu- 

 lar labial structures which apparently replace the lips. They 

 may be recognized by the fact that they are separated from 

 the papillae bearing labial rudiments by a groove; cephalic 

 probolae are known to occur only toincidentally with labial 

 probolae, pro.ject anteriorly and often bear the cephalic papil 

 lae at their bases { Acrnbelcs bodcnhcimeri). Lips, on the 

 contrary, bear papillae close to their apices. Another repre- 

 sentative of this odd group (Chambersiclla rodcns) possesses 

 six inwardl.v acting odontia internal to which there are si.\ cir- 

 ri ( ? cephalic probolae). When lips are present the full com- 

 ponent of cephalic papillae (1(3) are often observable but in 

 other instances they become difficult to recognize. 



Of the remaining families of the Rhabditoidea the Steiner 

 nematidae {Ncoaplrrtaiia glascri) have a rounded oral opening, 

 no lips, and the full component of well developed papillae and 

 the Angiostomatidae (Angiostoma pletlwdontis) have three in- 

 conspicuous lips and the full component of papillae while the 

 Drilonematidae are devoid of lips and have only the external 

 circle of papillae, eight in Dicelis nira and four in Vngclla 

 sccta. Drilonematids may also have large hook-like teeth pro- 

 jecting from the stoma {Vngclla sccta). 



Rejiresentatives of the Tylenchoidea have not been sufficiently 

 studied to make many statements regarding their cephalic 

 characters. As a rule the labial region is distinct, the lips 

 inconspicuous, six in number, and bearing four papillae and 

 the amphids. In a few forms such as Angiiina trilici and 

 Ratylcnchus similis an internal circle of six papillae have been 

 observed, these papillae being internal to the lips. In some 

 tylenchids such as Tloplntaimvs hradys the labial region is 

 striated and sujiported by a sderotized framework. In at 

 least one form (Nrotylrnchus abiilbnsiis) there is a medial )>air 

 of supplementary li|is between the original si.x lips. 



StrongyIjINA. Stri:ng)/liiidca. — The nuijority of representa- 

 tives of the s\iperfamily Strongyloidea have no lips or they are 

 greatly reduced or rudimentary. In all instances the ampliids 

 are dorsolateral or lateral and labial in position. 



In the family Strongylidae lips are absent and in their place 

 one finds the external corona radiata or leaf crown (Fig. ."iCi). 

 As we interpret these structures, they represent the divided 

 apical lobes of the original lips; they may number from six 

 to 40 or nujre. The labial region is generally set off from the 

 remainder of the body by a groove but it is not divided longi 

 tudinally as when large lips are present. Within this family 

 the internal circle is usually rudimentary or apparently absent 

 but it may be represented by reduced internolaterals (Slrongy- 

 liis cqiiinus). The external circle is reiiresented by four large, 

 often setose, sulmu'dian jKi|iillae each of which apparently con 

 sists of two origin;il papillae that have fused (dd. — Id. and 

 vv. — Iv.) ; ventrolateials are rudimentary. 



The closely relatecl family Syngamid.'ie su]iplies interesting 

 examples for c(»miiarison with tin- .Strong.vlidae. In Stcphanu- 

 nis dcniatus and Siingannis trachea the oral opening is sub- 

 hexagonal or one might .say there are six rudimentary lips 

 while in Dclclroccplialiis dcmidiatiis there are six distinct lobes 

 which might e({ually well be termed an external corona radiata 

 iir rudimentary laliial lobes. In all three ff.rms the internal 

 circle is reduced bnl, nevertheless, distinct and the external 



