curs in so iiiany otlior K'ciips (RlmlKlitoiilcii, Ascariiloidca, 

 Spiruioiiioa and Caniallanoiiica > is I'DnspiiUdiislv absent in the 

 StronK.vlina. 



Slniniiiihiitlfa. First stage stronK.vloids Ijave a stmiia iden- 

 tical witii that of KlKihililiti. 'I'liis stcinia uradiially c(ill;ipses 

 in the second stage and in tlie tliii'd stage it may simulate a 

 stoniatostyl. Cold) (1il:;,'i) descrilied tlie third stage larva of 

 Xicdliir ami ricdiiii.s as possessing a styli't liut as shown liy 

 Stekhoveu (l!'-t>) this was a false interpretaticui. The lunu'n 

 of the stoma is merely partly closed and non functional in this 

 stage, the so called stylet not heing protrusilile. A similar 

 appearance occurs in third stage Illiahdilis larvae when they 

 enter the resistant phase. 



In the adult stage there are two genera of the Strimgylidac 

 with a rhaliditdiil stoma namely CiiUnilriijihitriinx and PlKiiipi- 

 (/(KtlrDitf/jihis. Interiireting on the hasis of these two forms, 

 the chief part of the stoniatal wall, the so-called buccal cap- 

 sule of strongyloids corresponds to the amalgamate(l (iroto- 

 rhalidions of h'ltnbililis. The telorhabdions ir. some instances 

 l('illiniln>iih(irtinx. CiiUcoencIn'') may l)e represented by a 

 transverse sclerotized basal plate but iisually are not distin- 

 guishable. It has previously been noted that the external ca- 

 rona radiata seems to be homologous to the apical lobes of 

 the original lips. The internal corona radiata appears to be a 

 development of the cheilorlijibdions (Cnliiulrdphariin.r. Strrin- 

 finhis). Progressive shortening of the protorhalidions .accounts 

 for such forms as CylicDCi/iiii.t, Miirxhidiii and Orxdiiliafinstn- 

 miim. Thickening of the protorhalidions and dilation of the 

 protostom account for Stronguhis and its satellites. Teeth 

 originating at the base of the stonui (lancets') are a common 

 develo|iniint of tlw Strongylidae, Syngamidae and .^ncylosto- 

 m.atidae. Such oncliia are considered products of the telorhab- 

 dions. In ad<lition, one often notes a large dorsomedial tooth 

 or a tube in the dorsal wall of the stoma; this tooth or tube 

 is also thought to be a product of the telorhabdions though 

 it may extend to the anterior end of the protostom (Strniujii- 

 his) and is actually the duct of the dorsal esophageal gland. 

 It is often termed the dorsal gutter. 



Stomata in the Syngamidae are rather subglobular as in 

 many of the Strongylidae but they differ in that the protorhab- 

 dions have six longitudinal thickenings, two medial and four 

 sublateral ( Siinfinmii.i. Drhtroct phiiliif:. Slrphniiiini.i) . In the 

 Diaidianoceiihalidae (KalicephaJii.i) the protorhalidions are 

 split sagitally forming a pair of lateral jaws and tliej' usually 

 have four bmgitudiual thickenings on each side. In addition 

 the telorhabdions form a thick, sclerotized basal plate. 



In the Ancylostoniatidae the stoma usually has a distinct 

 dorsal bend and is asymmetrically developed as in Strnnpjihis 

 due to the large dorsal gutter. In addition there may be either 

 teeth (Anriiloxtoma) or cutting edges developed from the 

 cheilorliabdions on the ventral side. 



TricliDstriinfiiilinds and metastrongyloid.s are both character- 

 ized by marki'd stoniatal reduction. Usually there are no dis- 

 tinctly sclerotized stoniatal structures. However in a few 

 forms (Amidiislomiim, Fpomiilioitfomiim-Trirliostronfii/liilne 

 and Steniirus-Pseiidaliiilar^ .sclerotized protorhalidions persist 

 to the adult stage. In the Trichostrongyloidea .subventral lan- 

 cets arc occasionall.v present ( Amiilostomiim) and the dorsal 

 esophageal gland usually empties into the stoma. In the latter 

 instance its duct often takes the form of a sclerotized onchium 

 which may be the only sclerotized part of the stoma (Tricho- 

 Uipiriii. Tlaeniiinchiis). In metastrongyloids teeth of all forms 

 are apparently absent (Filiiriopf:is, Slntiirus, Dirljiocniiliis and 

 ^tt'tastrl>nfll|]|ls). It is interesting to note that trichostrongy- 

 loids revert to their ancestral stoniatal form, IDiabiliti.s, in the 

 first stage larva while metastrongyloids only ]iartially revert 

 in that stage for they have distinct cheilorliabdions and pro- 

 rhabilions of rhabditoid form but though the mesostom and 

 telostom are recognizable the rhabdions are non-sclerotized. 



Asc.\RiDiNA. Most ascaridins (Fig. 'i') either have a 

 rudimentary stoma or a weakly sclerotized vestibular region 

 but some representatives of the more ancient families, Thela- 

 sfoniatidae and Atractidae preserve a cylindrical rhabditoid 

 stoma. Thus Leidyiii ma cranifcra and Piubsfmaiiria vivipara 

 both have stomata in which the various stoiiiatorhabdions are 

 distinctly sclerotized. In Protrcllinn and Aoriinm of the 

 Thelastoniatidae one notes progressive shortening of the sto- 

 niatorhabdions and loss of sclerotization. The telorhabdions 

 may jiersist in the form of basal teeth or laminae or they nia.v 

 entirely disa[)pear. The dorsal esojdiageal gland never empties 

 into the stoma as in the Strongyloidea. In the Atractidae a 

 cylindrical jirotostom (TIfih, Prtthstmai/ria) ^ weakly sclero- 

 tized stoma with collapsed mesostom (Alractin) and vestibule 

 (Crossocrphahm) are all known to occur. In the O.xyuridae 

 the protostom is always greatly shortened, often feebly sclero- 

 tized (Kulrrohius) but the telorhabdions are commonly large 



and conspicuous laminae (Oxi/iiriti). The family Rhigonenia- 

 tidae is characterizeil by a rudimentary stoma surrounded by 

 esophageal tissue (vestibule). The stomatorhabdions an- non- 

 sclerotized, with the exception of the cheilorliabdions of h'lii- 

 fiont ma ; these latter take the form of three sclerotizi'd dentate 

 .jaws, internal to the lips. In Iclhiioci phaliis the stom.-ital 

 region of the esojdiagus is horizontally split forming paireil 

 .j.aws. 



The subfamily Subulurinai^ of the Asearidoidea is the only 

 group of that superfamily in which the stoniatal region is not 

 surrounded by esojihagcal tissue. Herein the short heavily 

 sclerotized jirotoscnn is followed by a dentate telostom (Siibii- 

 liira tli.itnn.s. Aulonorrphaliis pcramrlix) which is strongl.v remi- 

 niscent of OxiiKris and Enti'fdhiux. The other families have 

 weakly or non-sclerotized iirotorhabdions, the stoma coll.-ipsed 

 Mnd of subtriangular or triradiate form in cross section. In 

 the Cosmocercidae, Kathl.-uiiiilac and lleter.-ikin.-ie the base of 

 the vestibule (stoniat.-il region of esophagus) is evidenced by a 

 break in esophageal tissue at the original position of the telo- 

 rhabdions. In the Ascarididae, with the exception of Criisso- 

 plionis there is not the slightest evidence of the original stoma. 

 The esophagus seems to extend unintcrrn|ited to the tiase of 

 the liiis. The single exceptional genus gives the final proof 

 that the anterior end of tlie esojihagus of ascarids is homolo- 

 gous to the vestibule of cosmocercids and heterakids for in 

 Crnssophonix there is not only a distinct vestiliule but the 

 metastoni is dilated and distinct telorhabdions are visible. 



('.\M.\I,1,AX1N.\. The first superfamily, Camallanoidea, is 

 characterized by the presence of a well devidojied stoma in 

 most forms and at least a distinct vestibule in the remainder 

 while the second superfamily, Uracunculoidea, has a rudimen- 

 tary stoma, the stomatorhabdions are non-.sclerotized in all 

 forms (Fig. ^S). None of the adults in the Camallanoidea 

 have that which might be termed a rhabditoid stoma but Pro- 

 ramalhinus most clo.sely approaches it. In this form the stoma 

 is barrel-shaped, cheilorhabdicuis are not distinct, jirotorhab- 

 dions amalgamated and heavily sclerotized and followed by a 

 transverse ring-shaped telorhabdion. Li (193.T) has shown 

 that as in other groups the larva more closely apjiroaches 

 the rhabditoid stoma than does the adult for in the first 

 stage larva the stoma is much more narrow and cylindrical. 

 In adults of other genera of the Camallanidae (CarnaJlaniis 

 xweeti, C. americanus, etc.) the prostom is sagitally slit, form- 

 ing two lateral jaws; longitudinal ridges of the internal wall 

 of the protostom make their appearance and paired, sclero- 

 tized medial tridents are formed at the external surface of the 

 stoma. Somatic muscles are attached to both the tridents and 

 the exterior surfaces of the jaws. 



In the Cucullanidae one observes, though not as completely, 

 a repetition of the evolution in the f'amallanidae. Omcia is 

 the only form which retains the primitive, non-esophageal 

 tissue surrounded stoma but even in this case there is little 

 resemblance to the cylindrical stoma. Haploncma and Sciiralinn 

 ajipear to be products of some genus like Omcia in which the 

 stoma collapsed, stomatorhabdions degenerated and were cov- 

 ered with esophageal tissue forming a vestibule. Ciiciillanus 

 may be interpreted as more ancient than Omria in distinct 

 retention of pro- and meso-metarhabdions but less primitive 

 in that the entire stoma is surrounded by esophageal tis.sue and 

 sagitally divided forming lateral jaws. This is likewise one 

 of the very few exceptional cases wherein esophageal tissue 

 surrounding the stoma is not correlated with stomatorhabdiou 

 degener.'ition. 



SpiitiRix.v. Most members of the Sjiiruroidea (Fig. 58) 

 have a rather cylindrical stoma with strongly sclerotized proto- 

 rhabdions, but distinct cheilorhabdions are unknown. The sto- 

 mata of practicall.v all forms are specialized to some extent 

 and none can be regarded as prototypes of the superfamily. 

 However, various members of the Thelaziidae (Oxiispinira, 

 Axcarnps, Spirocerca and Ehabciocliona) indicate that a cylin- 

 drical protostom subdivisible into pro- and mesostomata and 

 reduced telostom with plate like telorhabdions were charac- 

 teristic of the ancestor. One cannot but be struck by the simi- 

 larity of the stomata of Lntu/ibucca and Ctilindrojinslir to 

 spiruroids both in this respect and in the tendency toward 

 bilaterality in cephalic structures. Nevertheless there is too 

 wide a gap between the Cylindrogasteridae (Fig. r)4") and 

 Spirurida for one to assume relationships at the present time. 

 In a few forms of the Thelaziidae (TheJazin. Pxriulafihiria) 

 the protorhalidions are shortened and amalgated but in the ma- 

 jority (Oxi/xpirura. Axcarnps, etc.) the protostom is elongated 

 and there are six oiichia at the junction of protostom and mesos- 

 tom. These oncliia may take varied forms, sometimes rounded 

 (Axcarapx) and sometimes bi- or trifurcate (Ciilicnspirura) : 

 in still other instances they may be dentate (Lciiirix) and 

 scmietinies opposed by medial iilates (Simondsia, Lciiiris). 



