In addition to the ordinary vaginal muscles there may 

 I'oe a large sphincter niusck at or near the vulvar open- 

 ing; such a muscle (Fig. 122 B) is present in Spironoura 

 and consists of one large muscle cell vifhose fibers are 

 on its external surface. A similar cell has been observed 

 in some free-living nemas {Chromadora sp. and Sabatieria 

 hihirida Figs. 120 B & E). Dilator muscles of the vulva 

 have already been mentioned (p. 43). In most cases 

 transverse or modified somatic musculature serves to 

 dilate the vulva. 



COMPARATIVE MORPHOLOGY 



Free-living Phasmidians. The female reproductive 

 system exists in its most simplified condition in the 

 Rhabditoidea. The vagina is always simple, moi'e or less 

 transverse to the body axis, flattened, without special 

 musculature and the uteri are likewise unmodified. Am- 

 phidelphic reflexed genital tubes are the rule, but mono- 

 delphic forms are also common. Studies on this group 

 include Maupas (1900) on Rliabditis dolichura, Kriiger 

 (1913) on R. aspcra {R. aberrans) , Schleip on Rhabdias 

 biifoiiis, Goodey (1935) on Brevibucca sapropltaga, Thorne 

 (1937) on Cephalobus persegnis and Steiner (1937) on 

 Eiicrphcihbus teres. In amphidelphic forms the vulva is 

 always more or less equatorial in position (about 40-65 

 percent) and oddly enough this position is retained in 

 the characteristically monodelphic- family Cephalobidae. 

 The vulva is preanal in other monodelphic forms such as 

 Brevibucca saprophaga (Fig. 117 C), Rhabditis lamb- 

 diensis and Longibucca. Apparently reduction from the 

 amphidelphic to the monodelphic condition is a sporadic 

 happening throughout the Nemata, and in many other 

 groups, such as the Rhabditidae the number of ovaries 

 has no bearing on the degree of relationship and in that 

 particular instance is not even a sound generic character 

 as may be readily ascertained by comparing the males 

 of the various monodelphic rhabditids {R. lamhdiensis, R. 

 monliystcra, R. spicidigera, R. ocypodis). Prior to its 

 use as a generic character at least one correlated, pref- 

 erably non-female, character might be found. In the 

 case of the Cephalobidae there is adequate evidence in the 

 way of stomatal and male characters to indicate that 

 ovarial reduction is a general character. 



The uteri are usually thin-walled, composed of a low 

 squamous epithelium in gravid females, while in quite 

 young females the lumen may be minute, the epithelium 

 thick. Monodelphic forms have a distinct postuterine sac 

 (Fig. 117 B) in the Cephalobidae but not always in other 

 families. A distinct seminal receptacle or spermatheca 

 may or may not be present. In Rhabditis strongyloides 

 (Fig. 116 A) there is a pair of seminal receptacles near 

 the vulva; in Brevibucca (Fig. 117 C) Goodey described a 

 pair of uninucleate uterine glands. The distal end of the 

 uterus functions as a seminal receptacle and fertilization 

 chamber in most rhabditoids (Maupas, 1900, Kriiger, 

 1913, Goodey, 1924) even though it is not ordinarily 

 distinctly set apart. Thorne (1937) has described a well 

 defined spermatheca at the ovarial end of the uterus in 

 Cephalobus persegnis (Fig. 117 B). 



Fig. 118. FEMALE REPRODUCTIVE SYSTEM. 



A-B — Tachygonetria vivipara {viviparous and oviparous females). 

 C — Rhigonema infectum (Distal region of uterus). D — Tetranieres 

 nouveli. E — Aruaria ontliuris (Vagina and uteri). F — Tetrameres 

 Inermis (Vagina and uteri). GH — T. fissispina (Vagina and uteri 

 showing "Bursa copulatrix" or seminal receptacle). I-L — Ancylos- 

 toma (luodenale (I — Diagram of ovejectors : J — Uterine end of 

 ovejector ; K — Cross section at level of II ; L — Cross section at 

 level of III). M — Pseudomermis vanderlindei (Vaginal region). 

 N-0 — Spirnra gastrophila (Ovejector). P — Hahronenia tnicrostovia 

 (Ovejector). Q — Hahronema vuiscae (Ovejector). R — Physaloptera 

 turgida. S — P. capensis. T — P. ttimefaciens. U — P. puradoxa. V — 

 Ahi}reviatn {tbbreviota, W — Physaloptera rebi. X — P. retusa. (R-X — 

 diagrammatic representations of vagina showing uterine branching). 

 Z — Hydromermis leptoposthia (Vagina). AA — Oesophagostomum 

 brevicaxdnnt. BB — Nrniatodiiits niauritanicus. CC-DD — N. fiUrollis 

 (DD. enlarged part of ovj. 1). EE — Protospirura nuniidiiu. FF- — • 

 Mesomerniis bursata (Vagina). GG — Gongylonema mueronatum 

 (Vagina) HH-II — O. scutatum (HH, Junction of vagina vera and 

 vagina uterina ; II, Junction of constricted and dilated parts of 

 vagina uterina). JJ — G. mueronatum (Vagina). KK — O. scutatum 

 (Vagina). LL, MM & 00 — Abbreviata poicilometra (Variations in 

 uterine origin). NN & PP-RR — Spirorerca hipi ( NN. adult: PP-RR, 

 fourth stage larva). A-B, D-H, BB-EE. GGKK, NN and PP-RR 

 after Seurat, 1920. Hist. Nat. Nem. Berberie : M, after Steiner. 

 1937. Skrjabin Jubilee; R-X. after Schulz. 1927, Samml. Helminth. 

 Arb. Prof. K. I. Skrjabin gewidmet ; Z-FF. after Steiner, 1929, 

 Zool. Jahrb.. Abt. Syst. v. 57 ; AA, after Schwartz and Alicata. 

 1930, J. Agric. Res. v. 40 (6) ; LL-MM & 00, after Sandground, 

 1936. Bull. Mus. Comp. Anat. Harvard, v. 79 (6). Remainder 

 original. 



The degree of development of the oviduct is seemingly 

 without significance in the Rhabditoidea since the ex- 

 istence of such an organ in some forms may be dependent 

 on the age of the specimen. Within the superfamily 

 diversity extends from no oviduct in Rhabditis lambdien- 

 sis and R. strongyloides to a well defined tube in Rhabdias 

 sphaerocephala. 



Diversity of ovarial form in the Rhabditoidea is limited 

 chiefly to length; the ovaries never become coiled or 

 greatly elongated organs as often occurs in the more 

 highly evolved parasitic groups. Maupas (1900) and 

 Kriiger (1913) have demonstrated that in Rhabditis 

 dolichura and R. aspera v. aberrayis the ovary produces a 

 limited number of spermatozoa prior to the appearance 

 of oocytes. This type of reproduction is termed syngonism 

 (Coblj, 1916) and is seemingly widespread among free- 

 living nemas. In the hermaphroditic Rhabdias, Schleip 

 (1911) found the syngone to produce spermatozoa and ova 

 alternately. 



The Tylenchoidea exhibit the same fundamental sim- 

 plicities in the reproductive system as do the Rhabditoidea, 

 but in this group monodelphic forms are much more 

 common and are generally placed in separate genera from 

 the amphidelphic types. The gonoducts may be either 

 outstretched (Ditylenchus dipsaci Fig. 117 K) or flexed 

 (Anguina tritici) or doubly flexed (Hexatylus intermedi- 

 us.). This group also contains the only prodelphic didelphic 

 free-living nemas, the highly specialized root parasites 

 of the genus Hetcrodera (Fig. 117 P) and in members of 

 the genus Hetcrodera the genital primordium is originally 

 equatorial as in other nemas. Some of the oddities (ex. 

 Sphaerularia, AUantonema) of the arthropod parasites 

 comprising the Allantonematidae have been previously 

 mentioned. Zur Strassen (1892), Leuckart (1887), Good- 

 ey (1930) and Bovien (1932) have made careful studies 

 of the reproductive systems of Bradynema, AUantonema, 

 Sphaerularia, Tripius, Tylcnchinema and Scatonema (Figs. 

 115 A-B, E & I-K). In all instances the reproductive 

 system is highly developed, and often the ovary becomes 

 coiled and the uterus enormous. Unlike most parasites, 

 these forms do not develop specialized mechanisms for 

 the ejection of eggs but instead there is often degenera- 

 tion and sometimes atrophy of the vulva and vagina. 



Free-living Aphasmidians. Since most modifications 

 of the reproductive system are related to increase in egg 

 production and are associated with life habits rather 

 than relationships, it seems best to cover the remainder 

 of the free-living nemas before proceeding to the para- 

 sites. As previously noted, Filipjev (1918, 1934) has 

 attached a great deal of weight to the position of the 

 utei'i and ovaries. It is true that in certain large groups 

 the female genital tubes tend to be extended while in 

 most nemas there is a flexure at the junction of ovary and 

 oviduct regions in the gonoduct which caused it to be 

 described as reflexed. Filipjev (1928, 1934) separated the 

 Monhysterata, (equivalent to our Monhysteroidea and 

 Axonolaimoidea and Microlaimidae) from the Chroma- 

 dorata (equivalent to our Chromadoroidea, Desmodoroi- 

 dea, and Plectoidea) on this basis, the female genital 

 tubes being outstretched in the former group while 

 they are "reflexed", or more properly speaking, flexed 

 in the latter group. In so far as this is a tendency 

 which is correlated with other characters, we recognize 

 the soundness of its use as a taxonomic character. How- 

 ever, it must be stated that there is nothing so very 

 fundamental in the differences, and other characteristics 

 must also be considered. In addition, separations on the 

 basis of the female reproductive system are not absolute 

 since undeniable exceptions to the rule are known. Thus, 

 the Comesomatidae, which otherwise show so many 

 characters in common with the Axonolaimidae (Monhys- 

 terina) on the one side and with the Cyatholaimidae 

 (Chromadorina) on the other side, present embarrassing 

 exceptions. The genera Dorylaimopsis and Laimella \vith 

 outstretched gonads must be ranged next to Mesonchium 

 with flexed gonads, and Comesoma minimum has an 

 anterior flexed and posterior outstretched gonad, while 

 other members of the genus Comesoma supposedly have 

 two outstretched gonads. Also, in the Microlaimidae 

 (Chromadoroidea), Microlaimu^ and Bolholaimus with 

 outstretched gonads must be ranged next to Achromadora, 

 Ethmolaim.us, Prodcsmodora, and Statenia with flexed 

 gonads. Halanonchus (Fig. 117 N) is an example of a 

 monhysterid with a flexed gonad. Similarly, the tendency 

 of the members of the subfamilies Monhysterinae and 



143 



