by Baker (1936) in Iliteraki.i' :ir.' ;ilsn rectal glaiuls ami 

 0(irresiio7id to the cells (if the "(;<'nit:il litjniTiciit " ilescriheil by 

 Mackiii. 



From these observatidiis, it aiipears that three rectal tjlanils 

 in the female ami six in the male is the rule for nu-nibers of 

 the Hhabilitoiilea ami Ascariilina and for at least sonic members 

 of the Si)iriiroidea. However, rectal Khinds appear to be totally 

 absent in tlie Tylenchoidea. The rectal ligament cells described 

 by Looss and Imminck for stronKyloids are in part rectal 

 glands. Such glands occur in representatives of all suborders 

 of the Phasniidia but appear to be absi'nt in a few isolated 

 types and gronps such as Ihaciiiiciihis, l)ir(ifihiii<i and tylen- 

 choids. I'erliaiis the absence of rectal glands in these forms 

 will be explained in the future on physiological grounds when 

 their function becomes known. 



In the Aphasmidia no single case has thus far been definitely 

 established of the existence of rectal glands. Tlxiugh men- 

 tioned by Kberth USfiH), Bastian (lS(!."i) ami de .Man (1H86) 

 it is notable that no later mention was made of such glands 

 by de Man (liHH") nor by Jiigerskiold (li)01). The best sub- 

 stantiated record of such occurrence is in Enoplus cnmmunis 

 as illustrated by de JIan (ISSi!). The writers have been able 

 to identify the numerous cells shown by that author as at- 

 tached to the rectum but all appear to be sejiarated from the 

 rectal lumen liy the cuticular rectal lining (Fig. 108 BB). 

 This is in sharp contrast to the established cases such as 

 Spironoiira and Ilvtiral-is (Fig. lOSN, 110 Y & MM) in which 

 there is a distinct break in the cuticle at the level of each gland 

 orifice. It is concluded that in Fnopliis communis the cells in 

 question are merely epithelial cells. Careful study of Ci/licolai- 

 miix and Thoracostoma by Jiigerskiold (1901) and Tiirk 

 (1903), of Trichurishy Rauther (1909, 1918), of Mrloncholai- 

 mii.i, Li'plosomatnm. Tripijla. Prionchidiis, Dioctoplnima, Soho- 

 Uphymc, Aphanolaimus, JJalichoiinolaimus, Paracanthonchits 

 and Dnri/Inimnpsis by the writers f;iiled to reveal rectal glands 

 in a single case. In Anaplcctiif: urnniihtsiis. female totomount 

 specimens apjiear to show three rectal glanils but we have not 

 been able to verify the point in sections. Pending further 

 proof it is concluded that aphasmidians are usually without 

 rectal glands. In the male of Dornlaimii.t prolificus (Fig. 21) 

 there is a group of four pairs of cells near the anterior end 

 of the prerectum which appear to be glandular; in living 

 specimens one may trace a slender tube leading from each cell 

 posteriad nearly to the intestine rectal valve where each tube 



*In Hfteraki.'i galUnae one finds si.x additional smaller cells in the 

 body cavity, a dorsal pair, one situated on each side nf and between 

 tlielarje pair of tandem dorsal rectal glands (Fig. 108, N P). and 

 two subventral pairs, one situated nn each side of each of the large 

 ventral rectal glands (Fig. 108 P, R). These cells seem to have ducts 

 into the cells to which they are attached. They may conceivably be 

 subsidiary rectal glands. Increase in rectal gland luimher from Ihree 

 to six and possibly to 12 seems to support the view of Macalister that 

 they are homologues of the malpighian tubules of insects. Martini 

 (191.11 aptly indicated the unicellular rectal glands of nematodes as 

 precursors of the groups of unicellular glands of Mnrrohiotufi which 

 in ttiTn are undoubtedly forerunners of the multicellular tubular glands 

 of other tardigrades. These last mentioned are. in turn, considered as 

 identical with the malpighian tubules of insects. Tliis view, though 

 questioned by Seurat (1920) seems logical in view of the fact that 

 multicellular tubular glands normally, in evolution, arise by reduplica- 

 tion of associated unicellular glands with common acini. 



papiUata (E — Cross section of male in region of cloaca and spicular 

 pouches; F — Longitudinal section in same region). G — Pnrascaris 

 f quorum (Longitudinal section through proximal end of spicule show- 

 ing spicular cells). H — Asrnris liimhrirnule-^ (Longitudinal section 

 through caudal region of male). I — Parasrariji equorum (Longitudi- 

 nal section through caudal region of male). J — (ioezia ^annulata 

 (Longitudinal section through caudal region of female). K — Paras- 

 carts equnruw (Cross section of tnale anterior to intestino-rectal 

 valve). L — Rondonia rnndoni (Lateral view showing vagina open- 

 ing into rectum). Jl-R — Heterakis ffrillhuie ( .\11 illustrations of 

 male. M — .\t level of intestino-rectal valve; N — At level or rectal 

 gland orifices: O — .\t level of preanal sucker; P — Reconstruction of 

 cloacal region: Longitudinal section at intestino-rectal viilvc showing, 

 sphincter muscle, double dorsal gland and secondary dorsal gland; 

 R — Cross section considerably anterior to intestino-rectal valve show- 

 ing paired subventral glands and their accompanying cells, secondary 

 glands). .S-V — Lpptnsomatum elonpntum v. acephnlntum (S-^Intes- 

 tino-rectal valve, inner cells are intestinal; T — Section following S: 

 U — Rectum showing epithelial cells: V — Preadult male showing spicu- 

 lar primordia). W — Doriilnimns stapnulis (Cross section showing 

 rectum of female). X-7,—3Ielo>u-holaimus prisliurus (X — Cross sec- 

 tion of male at level of infestino-rertal valve: Y — Cross section of 

 cloacal region of male showing spicules and gubernaculum : Z — 

 Longitudinal section of female: there is no evidence of rectal glands 

 or a break- in the rectal cuticle such as one would expect in that 

 case). A.\ — EnniKtoiinna amerirnnit (Cross sex-tion of male at 

 cloacal opening). BB-JJ — EnopJiis rmnmunis v. m^ridionnlis (BB — 

 Longitudinal section of female in rectal region, as in Z, there is no 

 evidence of rectal glands: CC — Cross section of preadult male show- 

 ing primordia of spicules and gubernacular crura; DD-JJ — Serial 

 sections through cloacal region of male, beginning postanal and going 

 anteriad. some sections omitted between most anterior sections). 

 G-I & K, after Voltzenlogel, 1902, Zool. Jahrb., Abt. Anat., v. 16; 

 J. after Hamann, 1895, Die Nemathelminthen v. 2: L, after Baylis, 

 1936, Ann. & Nat, Hist. s. 10, v. 17; remainder original. 



turns veiitr:id :inil ilisappears between the vas deferens and the 

 intestine; the homologues of the above mentioned cells are not 

 know II. 



The iiilestino-rectiil valve is a very simple structure, con- 

 sisting, in oligocytous forms such as Ulinhililis, of the poste- 

 rior p:irls of the jirerectal intestinal cells surrounded by a 

 sphincter muscle. In iiolycytous and myriocytous nematodes 

 the intestin.il cells in the valve region become much smaller, 

 more numerous, and ;ire often devoid of a bacillary layer. They 

 may form a valve either by rcHexure into the intestinal lumen 

 or "ext<>nsion into the rectal lumen (Fig. IIISQ ic 109W). 



The niusciilature controlling the intestino rectal valve, rec- 

 tum, and amis has already bei-n brietly discussed (ii. 43). The 

 existence of a uninucleate sphincter muscle was first made 

 known by .liigerskiold (18!»3, 1S94) and Cilson and I'antcl 

 (1894). Later workers have often confused other structures 

 with the siiliincter and described sphincter muscles with two, 

 four or more nuclei (Magath, 1919, in CamallanHs, and Chit- 

 wood, 19.'il, in M(irriicix). Reexamination of representatives 

 of all groups of the Nemiitoda by the writers establishes tlie 

 unicellul;ir sphincter as universally present. It is a circular 

 band of libers containing a single nucleus which may be dorsal, 

 ventr:il, or lateral in jiosition. Its innervation jirocess I'xtends 

 anteriorly to the dorsal nerve in Ascarix according to Volt- 

 zenlogel. This muscle closes the intestino rectal valve jireventing 

 reentry of materials from the rectum into the intestine during 

 defecation. 



The dejire.ssor ani, an II shajied muscle, is likewise unicellu- 

 lar and of universal occurrence. It is this muscle that elevates 

 the dors.-il wall of the rectum causing materials to be drawn 

 into the rectal cavity; it then elevates the )Kisterior lip of the 

 anus tlius permitting defecation. The rectum is devoid of circu- 

 lar muscles and for the most ]iart defecation is accomplished 

 by pressure. Subventral and subdorsal somato-intestinal mus- 

 cles (Fig. .")2) probably supply the pressure by dilating the 

 prcrectal lumen, thus drawing materials into that region from 

 the mid-region of the intestine and forcing them into the 

 rectum by relaxing at the same time that the rectal sphincter 

 relaxes and the anterior part of the depressor ani contracts; 

 by such means the rectal cavity is filled. Thereafter the rectal 

 sphincter contracts, the anterior part of the depressor ani re- 

 laxes and the posterior part contracts; pressure on the walls 

 of the distended rectum by the body tiuid causes it to collapse 

 and the waste products to be forced out. 



B. CLOACA 



The vas deferens enters the rectum from the ventral side in 

 males of all groups with the sole exception of the Trichuroidea. 

 In trichuroids Rauther (1909, 1918) found that the vas def- 

 erens enters the rectum dorsolaterally (Fig. 110 Z-DD). In 

 phasmidians the .junction of vas deferens with hind gut is 

 nearly simultaneous with or immediately posterior to the 

 intestino-rectal valve so that practically no rectum exists; 

 the whole of the hind gut is tlien transformed into cloaca. In 

 some aphasmidians, particularly enoploids, the vas deferens 

 is apt to .ioin the rectum somewhat more posteriad so that 

 both a rectum and a cloaca may coexist. 



C. SPICULAR POUCH 



With few exceptions, which will be discussed later, the 

 spicules enter the cloaca from the dorsal side immediately an- 

 terior to the anus. They develop in a pair of cell masses, the 

 spicular primordia, which develop as proliferations of the dor- 

 sal wall of the cloaca, first described correctly by Seurat (1920) 

 in Falcaiixtra himbilirnxix (Fig. ] 10 00). Schneider assumed 

 the presence of a single primordium in nematodes with two 

 spicules but this is incorrect. Previous to the formation of the 

 spicules the primordia arc without a lumen, as may be seen in 

 Enoplux (Fig. 108 CC), but later developmental phases in- 

 dicate that the spicuhir primordia should be interpreted as 

 instances of suppressed evagination followed by terminal in- 

 vagination. The primordia become differentiated in such a 

 manner that they form a pouch which contains the spicules. 

 As shown by Voltzenlogel (1902) the pouch is lined with a 

 cuticle continuous with th;it of the cloaca. It is covered by an 

 epithelium which is also continuous with that of the cloaca. 

 When two spicules are jiresent, the paired spicular pouches 

 always .ioin before entering the cloaca. In parasitic nematodes 

 this pouch and the protractor muscles of the spicules form an 

 obvious s]iiciilar covering termed the sheath. In free-living 

 nematodes the spicular pouch is often extremely delicate* and 

 easily overlooked. Possibly for this reason Tiirk (1903) denied 

 the existence of a pouch in Thoracostoma where it had been 

 previously observed ;ind illustrated by Jiigerskiold (1901). 



*The pouch wall and cuticle were inadvertently omitted in Fig. 49 

 E, L, M. They are delicate but nevertheless present in this form. 



llj 



