tials are distinctly separate from tlie laterodorsals and latero 

 ventrals in all members of the family but they are near the 

 size of the laterodorsals and lateroventrals in some forms, 

 {Thelazia californiensis, Psciidofilaria pertenue, Ascarops 

 strongylina) and are reduced or rudimentary in other forms 

 {Cylicospirura subaequalis, Spirocerca lupi) . In many of the 

 .species one notes six euticular projections of the prostom 

 (Spirocerca lupi, Ascarops strojigylina). As shown by Chit- 

 wood and Wehr (1934) the third stage larva of Phi/socephalus 

 scrahilii.-; has both the six rudimentary labial lobes and six in- 

 ternal euticular projections of adult Ascarops. The circumoral 

 membrane (labial lobes) disappear in the adult and the origi- 

 nal internal euticular projections assume the form of paired 

 trilobed lips which are termed pseudolabia. It is notable that 

 these projections bear the internal circle of papillae but the 

 papillae are rudimentary, not merely reduced as in other the 

 laziids. It is on the basis of these observations that the heads 

 of other spiruroids are interpreted. 



The family Spiruridae apparently contains tlie next most 

 primitive representatives of the Spiruroidea. In these forms 

 the pseudolabia are usually trilobed and with the exception of 

 Hedruris they do not bear the external circle of papillae. In 

 the Habronematinae (Habroneina) and Hedrurinae (Hedruris) 

 the median pairs of the external circle are very close together 

 or partially fused, there being an accompanying reduction in 

 the size of the dorsodorsals and ventroventrals while in the 

 Tetramerinae (Tetramcres americana) and Spirurinae (Proto- 

 spirura spp., Mastophorus spp.) there are four compound 

 papillae due to more or less complete fusion. Labial struc- 

 tures are highly varied in this group and very valuable as 

 generic and specific characters. Paired medial interlabia are 

 present except in the Spirurinae and their shape, relative size 



and complexity make very useful taxonomic characters (Tetra- 

 mcres, Hedruris, Seurocyrnea, etc). The pseudolabia are di- 

 verse in size, gross appearance and sometimes they ha\j char- 

 acteristic dentition. (Mastophorus vs. Protospirura) . Tetra- 

 mcres americana is anomalous in that the female has neither 

 pseudolabia nor interlabia, a sexual dimorphism coinciding 

 with the degeneration of the female to the form of a repro- 

 ductive sac. 



The family Aeuariidae is interpreted as being most closelj' 

 related to the Spirurinae of the family Spiruridae. As in the 

 latter subfamily, there are only four well developed papillae, 

 these being apparently the completely fused dorsodorsal-latero- 

 dorsals and ventroventral-lateroventrals. Unlike spirurids, the 

 pseudolabia of aeuariids are not trilobed and they bear the 

 four papillae. I'rojeeting posteriorlj- from the pseudolabia 

 aeuariids always have some type of euticular ornamentation 

 these ornaments taking the form of cordons in the Acuariinae, 

 a spined cephalic collarette in the Seuratiinae, and four va- 

 riously formed appendages in the Schistorophiuae. 



Passing now to the Gnathostomatinae we find that the pseudo- 

 labia have assumed a more massive size, become fleshy, but 

 retained their lobed character. There are four double papillae 

 in all forms, the degree of fusion varying in the different 

 genera. Of this family the Spiroxyinae is undoubtedly the 

 most primitive for it contains such forms as Spirojrys contnrta 

 which superficially resemble Protospirura and Mastophorus of 

 the Spirurinae. The subfamily Spiroxyinae differs from the 

 Spirurinae in tliat the pseudolabia are massive, and bear the 

 external circle of papillae in the former subfamily while they 

 are inconspicuous and the papillae situated posterior to them 

 in the latter subfamily. Gnathostomatids such as Tanqua 

 have similar papillae but the pseudolabia are more irregularly 



Cephalic regions in the Asciiridina. A-C — Thehi.'^toriuitidiic. 

 O-H — Atractidac. I-J — Rliiffoneniatidae. K-N — Oxyiiridae, O — 

 Cosniocercidae. I*-Q — Kathlaniidae. R-T — Heterakidae. V-\ — 

 Ascarididae. A — Lfidurifiiia cranifera ; B — Protrfllina fitirifln.na ; 

 (' — AoruruN philijfiiinansin ; D — Pvlchrorfiifiata sp.; E — Hefh 

 Airiiiirp}nnii : K — Atraclin sp. ; G — CrnHsfK'fiilinhtu vivipiints; H — 

 Prohtttttnijfria rivipttra ; I — Rhif/on^mn inffftlim; J — Icthyocephn- 

 lu8 sp. : K — Oxyuri« fqui; L — EiiterohiuK vermirulttrin ; M — As- 

 piculurU tetraptera; N — Dermatnxps rcUijrrn-; () — Cosmorcrcoidett 

 dukae ; P — Spironoura uffine ; Q — Cinsopln/fns rntteuy; R — Siihu- 



hirn itis-tinis ; S — A iilnmn'i'iilmhts pfrdiiirlis ; T — Ijrtfriikis jjiillimie ; 

 U — Porroi'iifcttm cheni; V — Poli/deijiliiK qundrit^orniji : \V — Pidy- 

 delptti« hoddaerti: X — Parttscaris equoriim ; Y — Ascaris himbri- 

 cnides. A-B — After Ohitwood, 1932, Ztschr. I'arasit., v. 5(1); 

 C — After Chitwood & Chitwood, 19114, Philipp, J. Sc, v, 52(4). 

 S — After Baylis, 19:i(l, Ann. & Mag. Nat. Hist, s, 10, v. .5. U— 

 After Hsu, 1933, J. Parasit. v. 19(4). V-W — After Baylis. 1921, 

 Parasit. V. 12(4). X — After Yorke & Maplestone, 192(5, Nema- 

 tode parasites of vertebrates. Remainder original. 



60 



