CHAPTER VIII 



THE POSTERIOR GUT 

 (STRUCTURES OF THE PROCTODEUM) 



Till' oxistoiU'O of :i riiiniilcti' diKostive tract tciiiunati'd l)v 

 HH aims and of separate sexes was diseovered b.v Tyson (1683) 

 in Axiuiris; lie probably observed tlie spicules also hut was un- 

 able to interpret tlieni correctly. Soon afterwards it was estab- 

 lished that the intestine of the female connects by means of a 

 valve or siiliincter with the |iosterior gut (rectum) and thence 

 with the outside through a ventrally situate<l anus. With one 

 exception, the female reproductive system never connects with 

 the rectum; in the genus Iliiiuiiniin TritrassDx, lilLMI (Atrac- 

 tidac) the vagina joins the rectum (Fig. lOSL) to form a cloa- 

 ca. This condition is api)roaclied in several other forms particu 

 larly Aonirusi oflilc (= .(. siibvloatiis Christie, lO.'?!, Thelasto- 

 niatidae) and Eustroniiiiliilcs tricolor Sugimoto, U)31 (Diocto- 

 phynuifidae"! but an internal .junction of vagina and cloaca 

 exists only in Hoiiddiiia. In the male, the reproductive system 

 always joins the rectum, forming a cloaca from the walls of 

 which various copulatory structures develop. Since there is 

 usually a definitely elongate tail, the anus or cloacal opening 

 is ventral. In exceptional groups characterized by the absence 

 of a tail, such as the Trichuroidea and I)ioetoi>hyuuit(>idea and 

 in scattered representatives of other groups the anus or cloacal 

 opening may be terminal or subterminal. Male strongylins can 

 hardly be placeil in this category since the dorsal ray repre- 

 sents the tail and the iicnital cone is developmentally a ventral 

 outgrowth of the cloacal lips. The intestino-rectal valve, cloaca, 

 spicules, gubernacuhini and telamon are all included under 

 the general heading of posterior gut since, with the exception 

 of the intestino-rectal valve, they are wholly formations of the 

 proctodeum. The valve is quite diverse, formed sometimes 

 chiefly, sometimes entirely from endodermal tissue, but in all 

 instances it functions as a part of the rectum. Other structures 

 are essentially modifications of the rectum and will be dis 

 cussed from that standpoint. 



A. RECTITM, INTESTINO-RECTAL VALVE AND 

 RECTAL GLANDS 



The rectum is a more or less flattened, subtriangular or irreg- 

 ular tube lined internally by a cuticular layer underneath 

 which there is a layer of large epithelial cells, and covered ex- 

 ternally by mesenterial and muscle tissue. Leuckart (1876) 

 was under the impression that the cuticular layer of the rectum 

 was continuous not only with the external cuticle but also with 

 the bacillary layer of the intestine. Voltzenlogel (i;t02) found 

 Leuckart to be in error regarding the latter connection. The 

 cuticular lining of the rectum ends slightly posterior to the 

 junction of mesenteron and proctodeum leaving the rectum 

 naked for a short distance. Though Voltzenlogel made this 

 observation on Ascaris it was confirmed by Martini (1916) for 

 Oj-i/iiris and the writers for such diverse forms as Metoncholai- 

 mns, CrphahibeUus, Dioctophjima and Trichiiris (Oncholaimi- 

 dae, Thelastoniatidae, Dioctophymatidae, and Trichuridae, re- 

 spectively). All investigators have found the rectal cuticle to be 

 continuous with the external cuticle. It is knowai to be cast off 

 at the molt with the remainder of the e.xuvium. Voltzenlogel 

 and Martini both ob.served that the fiber layers and striation 

 of the external cuticle cease at the inner side of the anal lips; 

 farther inward the rectal lining consists of cortical, matrix 

 and basal layers (see p. 30). However, there is considerable 

 thickening of the first two layers in most parasitic nenias. 



It is impractical to discuss the rectal epithelium without 

 first considerng the rectal glands since there has been much 

 confusion in interpretation. Walter (1856) was supposed by 

 Bastian (1866) to have first seen the large cells at the junc- 

 tion of the intestine and rectum in Cosmocerca trispinosa 

 (Oj-l/iiriii ornala) and to have mislabeled them nerve cells. Ac- 

 tually Walter was entirely correct; the structures he illustrated 

 were the paired preanal ventral ganglia. Shortly thereafter 

 Claparede illustrated the cells now known as rectal glands in 

 "Ascaris commutata" and "A. miicronatd" labeling them 

 anal glands. Since that time similar structures have been re- 

 ported from many parasitic nematodes, l^berth (1860, 1863) il- 

 lustrated "anal glands" in Ilcleralis vcsiciilaris, Draschia 

 megastnma, and Passaliinis ambifiuns ; Macalister (1865) men- 

 tioned thom in Atractis dactyhira and was the first to suggest 



that they might be liomologues of the Mjalpighian tubules of 

 insects; Hastian (1865) described anal glands in Anticoma 

 si)p., Linhomoriis, Ilalichoanolaimiis, and Cijntholaimus ; Biit 

 schli (1873) described anal glands in Khabditis aspcra : 

 Leuckart (1876) mentioned six anal glands in Anciihistuma ; 

 de Man (]88(i) described various cells .-iround the rectum in 

 Enoplus, Onrhohiiinus, and Anticoma as anal glands; Hesse 

 (1802) working on Parnscaris interpreted the large cells as 

 "Gewebepolster" cells; Augstein (18!t4) observed anal glands 

 in Dictjiocaidiis filaria; Shijiley (18SI4) described anal glands 

 in Toxascaris Iransfiii/n but later (1897) presumed them to be 

 identical with the giant " biischelformige Organo" ((.'oelomocy- 

 tes, see p. 45); Jagerskiiild (1893, 1894) described anal glands 

 and a unicellular sphincter muscle in Contracacciim clavatiim: 

 Ilamann (1895) gave a very good description of both rectal 

 glands and rectal epithelium in Gocsia (Anisakinae) ; Ehlers 

 (1899) and .lerke (1901) mentioned rect.-il glands in Oxiiuris 

 f(;«i; Looss (1901) described cells forming a " rectal ligament " 

 in members of the Strongylidae considering the whole group 

 of cells in this region as being non-glandular; Voltzenlogel 

 (1902) gave an excellent description of the rect.al glands, rectal 

 epithelium, etc., of Ascaris; Looss (1905) denied the existence 

 of recta! glands in Ancylostoma and interpreted these cells as 

 part of a "rectal ligament" which view was concurred in by 

 Imminck (1924) working on SIrongybis, Tornf|uist (1931) 

 working on CiiciiUanns and Camallaniis and Mackin (1936) 

 studying Spironoiira ; Martini (1916) published thorough de- 

 scriptions of the rectal glands, epithelium and musculature of 

 0.ryuris; finally Magath (1919) considered the rectal glands as 

 sarcoplasm of the sphincter muscle. 



Controversy over the function of cells of the rectal region 

 has confused the picture, especially since some workers deny 

 the existence of fun(?tiona! glands opening into the rectum. 

 Recently the writers (1930, 1931, 1933) observed the orifices of 

 such glands into the rectum in Kliabilitis, Hetcrakis, Macracis, 

 Cephatobclhis, and Eystrifinatliiis (Rhabditidae, Heterakidae, 

 Oxyuridae and Thelastoniatidae respectively) and similar gland 

 orifices were reported by Baker (1936) for Hetcrakis. It does 

 not, however, necessarily follow that all of the structures in 

 the past termed glands are homologous with the structures de- 

 scribed by the above mentioned authors. As will be seen later, 

 rectal glands are by no means a universal feature in nematodes. 

 However, it is considered certain that the structures described 

 by Jager.skiold, Hamann, Voltzenlogel and Martini are rectal 

 glands. 



Hamann reports that the rectal epithelium of Goesia is 

 composed of two pairs of cells, one pair anterior and one pair 

 posterior to the rectal glands (Fig. 108J). In Ascaris, Volt- 

 zenlogel found four large epithelial cells forming an anterior 

 circle (Fig. 1081) and additional cells posterior to them but 

 the latter were not constant in position. In Oxynris Martini 

 describes the rectal epithelium as composed of seven cells, an 

 anterior ring of three, (one dorsal and two subventral) and 

 two pairs of cells arranged in tandem posterior to the first 

 group (Fig. 109W-X). In females of Goczia, Ascaris, and 

 Oxyiiris there are three rectal glands projecting into the body 

 cavity and having processes which penetrate the rectal epitheli- 

 um. Voltzenlogel was the first to show that there is sexual di- 

 morphism in the number of rectal glands; he reported six rectal 

 glands for male ascarids; Martini later found the same number 

 in males of Oxyiiris. 



Confusion in regard to the structures has been due to two 

 factors; the rectal glands may be embedded in the lateral and 

 dorsal chords or they may be associated with the vas deferens. 

 Thus Mackin described tlie rectum of Spironoiira as composed 

 of 10 cells in the female, three forming a "rectal ligament," 

 and 14 in the male, two in a dorsal "ligament," two in a 

 "genital ligament," and one in each of two ligaments extend- 

 ing to the lateral chords. All of the cells designated "ligament 

 cells" liy Mackin are rectal glands; those of the "genital 

 ligament" are embedded in the wall of the vas deferens but 

 have separate orifices into the rectum (Fig. IIOMM). The 

 "small ej.'iculatory glands" described by Chifwood (1930, 

 1931) in h'liabihlis (Fig. 3, ej 2) Mnrinris and UrtrraVis and 



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