approaching in pairs), six medials partially or completely 

 fused) or four (ventrolaterals apparently absent). 



Metastrongi/loidea. Members of this superfaniily have 

 neither the corona radiata of the Strongyloidea nor the cephalic 

 inflation of the Trichostrongyloidea. Lips, if present, are mucli 

 reduced except in Hetastrongylus which has six massive lips, 

 the largest of which are lateral. The oral opening is usually 

 rounded and the labial rudiments, if present (Filariopsis ara- 

 tor, Steniirus sp.) set somewhat far back from the mouth and 

 bear upon them only the internal circle of papillae. The same 

 tendency of papillary reduction and fusion observed in the 

 Strongyloidea and Trichostrongyloidea follows also in this 

 superfaniily, medials of the external circle being smaller as 

 are also the ventrolaterals {Filariopsis, Stenurus, Dictyocauliis, 

 Metaslrongylus) . 



AsCABiDiNA. Members of the Asearidina usually have three 

 lips, one dorsal and two subventral (Fig. .57). While the in- 

 ternal circle of papillae is always reduced or rudimentary the 

 two supcrfamilies differ as regards the external circle. In the 

 Oxyuroidea the ventrolateral papillae are ahvays rudimentary 

 or absent while in the Ascaridoidea these papillae are well 

 developed. 



Oxyuroidea. In this superfamily the Thelastomatidae appear 

 to be most primitive as regards cephalic papillae, for tlie ex- 

 ternal circle consists of eight quite separate papillae practically 

 equal in size (Leidynciiia appendiculatum, ProtrclUna flori- 

 dana, Aoriirus philippinensis) . However, in this family lips 

 are usually absent, tliere being a delicate circumoral membrane. 

 In a few exceptional forms three reduced lips may be preserved 

 (Fontonrma brachyyastcr) and sometimes a lobing of the cir- 

 cumoral membrane may give the appearance of six reduced 

 lips, two medial, four submedial (Aoriinis pliilippine7isis) . 



The family O-xyuridac appears to be a direct development 

 of the Thelastomatidae in other structural characters but the 

 fact that most members of this family retain three distinct lips 

 (Enterobiiis vcrmicularis) and one form (Oiryuris rqui) pre- 

 serves the rudiments of six lips, seems to indicate that they 

 must have originated rather early in thelastomatid phylogeny. 

 Unlike thclastomatids, oxyurids have only four well developed 

 papillae of the external circle. We interpret these as com- 

 pound papillae formed by reduction of the mediomedials (dd. 

 and vv.) and their complete fusion with the lateromedials (Id. 

 and Iv.). Secondary labial changes produce forms with two 

 lateral lips by disappearance of the dorsal lip (Macracis mon- 

 liystcra) and others with four lips by division of the dorsal lip 

 (Aspicnluris irtraplcra) . Perhaps the strangest case of labial 



modification occurs between the closely related genera Well- 

 coinia and Syphacia. In the former genus there are the usual 

 two subventral and one dorsal lip while in the latter genus 

 there is one ventral and two subdorsal. This absolute reversal 

 in symmetry of the lips is not accompanied by reversal in 

 other organs; the dorsodorsal papillae of Syphacia are on the 

 subdorsal lips, each of which has two compound papillae and 

 an amphid in the usual symmetry ; the ventral lip has no 

 papillae. 



The family Rhigonematidac is like the Oxyuridae in number 

 of cephalic papillae and the subfamily Rhigonematinae con- 

 tains forms with the common three lip symmetry (Rliigoncma 

 infcctum) . However, the other subfamily, Icthyocephalinae, 

 presents a startling modification of symmetry. The head is 

 divided forming two .jaws and contrary to general opinion 

 and to all other nematodes, the jaws are dorsal anil ventral 

 instead of lateral. The four compound papillae and lateral 

 pore like amphids retain their normal positions not being modi- 

 fied by the change in symmetry. 



Members of the Atractidae are the most diversified in ce- 

 phalic characters of the whole suborder Asearidina. Many of 

 these forms are highly specialized and yet one must concede 

 them a very ancient position in the Oxyuroidea very close to 

 the Thelastomatidae. Like the oxyurids and rhigonematids 

 they have only four compound papillae in the external circle 

 and in this respect the thclastomatids should be more primitive. 

 Six, three, and two lipped forms all occur in the Atractidae. 

 The genus Atractis has six well developed lips not unlike 

 Rhabditis tcrricola, while Crossocepltaliis has three lips like 

 oxyurids. Pidchroce phala retains the three lips but has in ad- 

 dition cuticular projections from the labial region which may 

 take innumerable forms but each element is grossly similar to 

 an insect wing. Ilcth, on the other hand, has two lateral lips 

 with corrugated edges and is provided with a spinate cephalic 

 collarette, while in Labiditni.s f/iilosus the dorsal lip is replaced 

 by a tuft like appendage. In the ransomnematids {Heth, 

 Piilchrocephala etc.) the highly specialized or ornamental 

 cephalic structures are confined to the female and do not make 

 their appearance until the last molt. 



Ascaridoidea. Members of the Ascaridoidea generally have 

 three large conspicuous lips; the ventrolatei'al papillae and 

 the other members of the external circle are all well developed. 

 Throughout the entire group the medial pairs of the external 

 circle are incompletely fused. One cannot assume ascaridoids, 

 having the full component of papillae, arose from oxyuroids 

 liut neither can one assume the reverse for the entirely sepa- 



FlG. 55. 



Ceiilialic rfjrioii in the T,vI('iichoi(iae. A-K aiui (> T' — T.vlen- 

 chidat*. M-N — Alljintoneniatidnc. A — Aiis/uitm tritivi; B — 

 Ditylf.nehus dipfraci; C-]0 — Neutj/lpnchutt abulhomi.s (('-D, fe- 

 mnle; K, ninle) ; F-H — liottilrnrUun ftimiUs (F, ft^iniile at last 

 molt: O. upper, head nf adult fiMuale and l()wer, adult male; 

 H, adult female); I — I'drati/lriieh ii.s wiU'rophnUon ; J — Aphelen- 

 ehoidt's paridiniiH : K — Aplu'lfnrliu.s avenue; L — Uelerotf/leii- 

 chus uberrans ^ adult fiee-livins feuiale) ; M — AUuntnnemu 

 mirahile (adult free-living female); N — Choiulronemu pufi.sali; 



O — Hnpluluiuius brudjis : V — liiili/leiielnis rDhu.^ilus. A — After 

 Stciner, 1925, rhvtiipalh., v. 15(<l). CI) — .\tler Steiner, 

 19:il, J. Wash. Aead. Sc, v. 21(21). E — After .Steiner and 

 Buhrer, l!i:t2, J. Wash. Aead. Sc., v. 22(l(i). F-H — After 

 ■Steiner and Buhrer. lilil:!, /tschr. Parasitenk., v. 5(2), Jj-M — 

 After Bnvien. 1{);J7, .Scime t.vpes of association between nema- 

 todes and insects. N — After Christie and Chitwood, lOill, J. 

 Wash. Acad. Se., v. 21(15). O — .-Vfter Steiner and Le Hew, 

 li>:j;j, Zool. Anz. V. 101(9-10). Reiuaituler origitial. 



58 



