liilifil :ui(i i>(istoii(ir to tluin tlicir is a laiKO c<'|i1i:iIk- Imlli 

 fornioil l)V till' anterior expansion iif four internal posteriorly 

 extending eloseil saes, the l>allonets (Ttinqtm). Xeitlier tlii' 

 Anevracaiitliinae nor the Spirox.vinae have a ceplialie Imlb 

 liiit some authors have reeoriled hallonets in Anciirafantliiis. 

 The eeplialie liulti apjiarentlv t'linetions as a hohlfast. beint; 

 eollapseil when the anti'rior enil is inserted into the niueosa 

 and thereafter liein^; inllated. Spines or ret rose annnlation 

 are provided to aid in this funetion. Anciiractuilhii.i with four 

 posteriorly direeted eephalie a|ipendages resembles Scliistoro- 

 fihiis of tlie Aeiiariidae but the ineoniplete fusion of the ee- 

 phalie papillae and the lobed tleshy i>seudolabia seem to de(i 

 nitely plaee it in the (inathostoniatidae. 



The I'h.vsalopteridae ap|iarently represent the liiial eonelu 

 sion of evohitionary tendencies in the Spiruroidea. Here we 

 find paired, massive tleshy, unlobed pseudolabia bearing both 

 amphids and four completely fused compound pajiillae (latero 

 dorsal dors<idorsal and lateroventral vi'utroventral ). Tlie va 

 rious species of this family have been divided into genera by 

 Schulz (1027) on the basis of their dentition. The genus 

 Pliysalopit ra is characterized by the presence of four teeth on 

 the internolateral face of each pseudolabium, an internal 

 group of three, two being sublateral and one lateral, an<l a 

 single externolateral tooth. Tliiihiinnrn is similar but the 

 teeth on one side are always rudimentary. Abbrcviata, has the 

 same later.-il teeth but instead of sublaterals the entire margin 

 of each pseudolabium is dentate and there are four double 

 submedial teeth. Whether or not these teeth correspond to the 

 original pseudidabial lobes is problematical but their develop- 

 ment as laliial structures seem to place them clearly in the 

 category of otloiilin which stateuu'nt also applies to the teeth 

 of Protosjiirura, ^^astophorus, Odontospirura, etc. of the fam- 

 ily Spiruridae. 



FUarioidra. Many tilarioids have neither lips, pseudolabia, 

 nor any other types of labial structures (Fig. 59), Such 

 forms (IJirofilaiia. Dipvl alone ma. Elacophora) are placed in 

 the family Dipetalonematidae. They are characterized by the 

 absence of any structure which might be conceived to be of aid 

 in feeding or penetration of tissue. The oral opening is 

 roundeil and bordered by a very delicate cireumoral membrane. 

 The ma.iority of the remaining forms have some type of ce- 

 phalic armature, such an armature sometimes taking the form 

 of a cireumoral elevation which may bear lateral (Uicluilo- 

 nenm) or other anterior tooth like projections (pseudonchia), 

 sometime taking the form of a sclerotized* helmet (Squamo- 

 filaria), sometimes having both cireumoral elevation and hel- 

 met (Dichrili))ir)iia), and sometimes taking the form of lateral 

 sclerotized tridents (Diplofriaena). These forms are all in- 

 cluded in the family Filariidae. The remaining two families, 

 Stephanotilaridae and Desmidocereidae each contain but one 

 genus and may later be more closely associated with the other 

 two families. The former family has one or two circles of 

 cephalic spines while tlie later is devoid of external armature 

 but possesses two internal cutieular pro.jections of the prostom 

 which ma.v lie homologous to the pseudolabia of siiiruroids. 

 In the number of cephalic papillae the super-family Filarioidea 

 is a remarkably constant group. There are always eight sub- 

 equal large papillae which tend to take the form of two circles. 

 However, we interpret these papillae as representing a sub- 

 divided external circle and the dorsodorsal and ventroventrals 

 are usually anterior (Dicheilonema, Dirofilaria) to the latero- 

 dorsals and lateroventrals. The internal circle is apparently 

 absent except in a few genera where it is represented by re- 

 duced internolaterals (DipetaJancma. Litomosa, and Desmido- 

 circa). Many writers would interpret the four anterior papil- 

 lae of tilarioids as the internal circle but we cannot do this 

 because in our comparative studies it is notable that throughout 

 the entire Phasmidia there is a tendency toward reduction in 

 papillary size. This tendenc.v affects the internal circle first, 

 and tliereafter the externomedians. Furthermore, the rear- 

 rangement of the external circle into two circlets as a tendency 

 in the order Spirurida is noticeable in iticroplcura (Dracun- 

 culoidea) and Pst mlnfilaria (Spiruroidea) in both of which 

 there is the full component of papillae. 



R. APHASMIDIA 



Aphasniidians have externally modified amphids in all except 

 the parasitic forms and even in these the modification per- 

 sists in many of the Mermithoidea. Filip.jev (1918, 1929, 19.S4) 

 used the morphology of the amphiils ;is one of the prime char- 



*The term sclerotized i.s used in ttie reiiminder of this text to indi- 

 cate hardening witliout siRnif.ving tlie chemical composition. Eventually 

 the chemistry of specialized cutii^ulnr structures will be discussed. 

 Though many nemic st-mrtures superticially resemble cbitin. this sub- 

 stance has been demonstrated only in the egg shell 



Meters of nia.joi groups. .More recently Stckhoveii «nd de 

 Coiiinck (19.'i:t) have rcalliriiied such usage with modification. 

 Of the many amiihidial variants, there are tliree primary types 

 in the .\ph:isinidia, these being the .'spiral, circular, and cya- 

 lliiform (iiocketiike). One easily recognizes transitions from 

 (ini.ipin to (lispirc .-ind mull ispiri , and other series from unispire 

 lliiougli (iiKsliiin marl:, to sIiiplicril.-< criiok : these latter may be 

 termed modified spir;il amphids. Transition lietween unispire 

 and circular is also an obvious step often indicated by ;i per- 

 sistent break in the circle. Stekhovcn and de Coninck (1933) 

 further derive the rcniform (transversely elongate) amphids of 

 Oiritmailnra from the circular amphids of Mwralaimiin. In- 

 Icrrelationsliip of these amphidial types seems scarcely ques- 

 tiouiible and this fact is used jis a basis for the order Chro- 

 madorid.'i. 



The cyathiform type of aiiipliiil. characteristic of the order 

 Knoplida. seems at first glance to be of an entirely different 

 formation but as we sli;ill see later, it also appears to liave 

 been derived from something close to the unispire. 



Cephalic sensory org.-ms in the .\pliasmidia universally have 

 one jioint in common, the lateral p.-ipillae of the external circle 

 are externolateriil rather than vcntrol.ateral in iiosition. This 

 is correlated with the post labial position of the amphids and 

 is, perhaps, more primitive than the rhabditoid (and general 

 lihasmidian) arrangement. The size of cephalic setae presents 

 another interesting field for observation; the external circle is 

 always larger than the internal circle and whether the external 

 circle is subdivided {Plectus, laimclla) or not (Paracanlhnn- 

 cltiis, .tnlicoma, Theri.<itus) the elements are always of two 

 sizes. If there are four large setae these are laterodorsal 

 and latcroventral. but if there are six they are dorsodorsal. 

 ventroventral and externolateral. The coni|ionents of the in- 

 ternal circle are often papilla like and h;ive been overlooked 

 by many observers; the smaller members of the e-xternal circle 

 may also be overlooked. It may be stated, however, that with 

 scarcely an exception the full component of cephalic papillae 

 is present. Supplementar.v cephalic papillae or setae also 

 occur and are very apt to cause confusion in the nomenclature. 

 Two or more pairs of sublateral setae next to the ampliid 

 (paramphidial setae) are of the most common occurrence such 

 being quite common in the Axonolaimoidea and Monhysteroi- 

 dea. The only ea.se of apparently true duplication of cephalic 

 setae occurs in some monhysteroids {Tlicristii.i) in which the 

 externolaterals are double. Mergence of somatic with cephalic 

 setae (or papillae) is an unusual but not uncommon phenom- 

 enon. In such cases (Eiistrongylide.i, Mononchus, Metachro- 

 maihira) the .sublateral or submedial somatic setae extend to 

 the head region and become confused with the external circle 

 of cephalic setae. Such added setae may become so numerous 

 as to completely obscure the normal symmetry (Slrincria). 

 Fusion of cephalic sensory organs, so common in the Phasmidia, 

 seems to be non-existent in the Aphasmidia. 



Labial structures are entirel.v too diverse in this class for 

 one to make satisfactory general statements. Both six and 

 three liiiped forms occur in the two orders but six lips aro 

 definitel.v preponderant. 



MONHY.STEKIN.V. In cephalic sensory organs the suborder 

 Monhysterina (Fig. 60) exhibits no real distinguishing char- 

 acter from the Chromadorina, one can speak only of tendencies. 

 The lips may be well developed, entire (Plcctu.<i), they may be 

 represented only by the apical lobe (Axonolaimiis) or they 

 may be absent (SphaeroIaimii.<!) . In no instance are lips ob- 

 viously replaced by cheilostomatal or prostomatal rugae. 



Plectoidca. The Plectoidea is undoubtedly one of the most 

 interesting groups of the entire Aphasmidia for it contains the 

 potentialities of every structural diversity of the subcla.ss. In 

 tactile organs the great majority of the forms are uniform hav- 

 ing an internal circle of six pajiillae and a subdivided external 

 circle of six papillae (dd., vv. and el.) and four setae (Id. and 

 Iv.). Paramphidial setae are unknown in the group. The di- 

 versity of amphidial form in the group provides clues to the 

 relationships of the whole Aphasmidia. In Anonehus mirabilis 

 and Plectus rliisophilus one sees the typical unispire amphid, 

 a double contour structure, each edge being the side of the 

 groove. In Aphan<ilaimu.<i aqualicu.<t and CaiiKicalaimux pry- 

 therchi there are nearly closed, unispire amjihiils of single con- 

 tour but if one observes these en face, one sees that the central 

 protuberance is present. These amphids are also unispire 

 grooves. The broken circle (singh' contour) amiihid of L<p- 

 tolaimu.i maximu.i has not been studied en face but other species 

 of the genu-s are known to have unispire amphids. Anaplcclus 

 (jranulu.iux (Phctu.K graiiulo.suK) is the final summation of all 

 others for it combines features of the circular, unispire and 

 cyathiform amphids. One might even term it a "universal 

 amphid." At the surface it is a transversely elliptical, but 

 internally it is both unisiiire and cyathiform. One might argue 



61 



