4. Asymmetric System. A single lateral canal confined 

 to one (usually the left) lateral chord, is apparently a 

 reduction phenomenon which arose twice; (a) in the 

 Ascarididae and (b) in the Tylenchoidea. 



(a) Shift of the sinus nucleus to the left lateral 

 chord in Ascaris with submergence of the sinus to a 

 minor role supplies a clue as to the origin of the anisakid 

 system. Representatives of this group have been studied 

 by Mehlis (1831), v. Siebold (1838), Schneider (1866), 

 Cobb (1888), Hamann (1895), Jagerskiold (1893, 1894, 

 1898) and Mueller (1927). In such forms the excretory 

 pore is often situated far forward, even between the 

 subventral lips (Anisakis simplex). The system as ob- 

 served in ContracaecKiH and Anisakis consists of a ter- 

 minal duct connected with a lateral canal in the left 

 lateral chord, this canal being greatly enlarged and 

 having numerous side branches (Fig. 114 O). As in 

 Ascaris, branching is most noticeable at the level of the 

 gigantic sinus nucleus. According to Jagerskiold and 

 Mueller the entire system consists of a single cell served 

 by the one large nucleus (Fig. 114 H-J), but this seems 

 improbable in the light of other observations which have 

 shown that the terminal duct is a separate entity. 



Hamann (1895) found an even greater reduction in 

 the excretory system of Goezia annulata. Here the entire 

 system is formed by a short tube (Fig. 113 00-PP) 

 which begins in the left lateral chord and ends between 

 the subventral lips. This tube is composed of three 

 cells in tandem, the lumen being intracellular. 



4b. The tylenehoid system (Fig. 9C) was first noted 

 by Davaine (1857) and later observed by Biitschli (1873), 

 Strubell (1888), Debray and Maupas (1896), and Cobb 

 (1914). Unlike the situation in the Anisakinae, there 

 is no shift anterior of the excretory pore correlated with 

 asymmetry. In these forms there is a very well devel- 

 oped, long terminal duct leading posteriorly to one lateral 

 chord. This chord may be either right or left, usually 

 right but the side varies not only with species and 

 strains but also among individuals of a given popula- 

 tion. The terminal duct apparently has one small nucleus 

 in its wall and the lateral canal contains a gigantic 

 sinus nucleus (Fig. 113 H). Tylenchoids also differ 

 from Anisakinae in that the lateral canal extends anteriad 

 to its junction with the terminal duct. Cobb (1914) 

 described in this group the only nema thus far known 

 with a posterior ventral excretory pore, Tylenchidus 

 semipenetravs, and in this form there is sexual, dimor- 

 phism, the excretory pore being near the middle of the 

 body in the male. 



There is no evidence of relationship between these 

 two asymmetric systems any more than there is between 

 the forms grouped under the inverted U system or the 

 H system. Undoubtedly we would derive 4a from 3 

 (ascarid) and that from lb just as 4b would be derived 

 directly from la. 



Adenophori (Aphasmidia) 



Thus far, only one type of non-canalicular excretory 

 system is known, that being the simple ventral gland 

 cell as first observed by Eberth (1863) in Oncholaimus, 

 Enopliis and Enchelidium, (Enoploidea) . Shortly there- 

 after Bastian (1866) described the same type of cell 

 in Cijatholaimus (Chromadoroidea) and Sphaci-olaimus 

 (Monhysteroidea). Since then through the work of de 

 Man, Cobb, Steiner and others, we have come to view 

 this as the typical aphasniidian system. In it there is 

 often a terminal ampulla (Fig. 112 0-P) and the 

 excretory cell may have a greatly elongated neck (Fig. 

 114 Q) but it is never lined with a cuticle except at 

 the terminus. It might be regarded as corresponding 

 either to the sinus cell or the terminal duct cell. Be- 

 cause of the absence of lateral canals, which we assoiiate 

 with the presence of a sinus cell, we prefer the latter 

 interpretation. According to this view the terminal duct 

 cell of the Secernentes system is homologous to the 

 ventral gland of the Adenophori. In chromadorids and 

 desmodorids there are often one or more small elongate 

 bodies posterior to the excretory cell which have been 

 considered secondary or auxiliary excretory cells (see 

 Steiner, 1916) but more recent study has shown them 

 to be coelomocytes without apparent protoplasmic con- 

 nection with the excretory system. 



De Man (1886) found the ventral gland of Enophs 

 communis to be lobed in such a manner as to justify the 

 term H-shaped (Fig. 114 U). Some more recent workers 

 such as Wiilker and Stekhoven (1933) have interpreted 

 the structure found in Enoplus, as an early stage in the 

 origin of the Il-type excretory system. The writers re- 

 gard the lobation in Enoplus a coincidence since it would 

 not account for the existence of a cuticularly lined 

 terminal duct. The typical ventral gland has been de- 

 scribed in representatives of the Chromadoridae (Fig. 

 114 X), Microlaimidae, Cyatholaimidae, ? Desmodoridae, 

 ? Epsilonematidae, ? Draconematidae, Camacolaimidae, 

 Axonolaimidae, Comesomatidae, Monhysteridae, Linhom- 

 oeidae, Enoplidae, Oncholaimidae, and Ironidae. There 

 is scarcely a group, however, in which a ventral gland 

 has been found in all genera. Perhaps this is due to 

 delicacy of the tissue which changes quickly on fixation. 

 We have been unable to locate a ventral gland cell in 

 Ethmoluimits revalie7isis, Monoposthia hexulata, Monliys- 

 tera cambari and Theristus setosus even after careful 

 examination of serial sections. 



Jagerskiold (1901) associated the existence of sublateral 

 hypodermal glands with degeneracy of the excretory 

 system in aphasmidians in general and Cylicolaimiis 

 magnits, Thoracostoma spp. and trichuroids in particular. 

 While it is true that h.vpodermal glands are very well 

 developed in some such forms, they are no more so than 

 in species with a distinct ventral gland such as Acantkon- 

 chas vivipariis (Fig. 15 N). t'urthermore, sublateral 

 hypodermal glands are now being found in more and 

 more groups in which they had been overlooked (linhom- 

 oeids, oncholaimids, dorylaimids, microlaimids, chroma- 

 dorids). 



Nevertheless, it seems to be an established fact that 

 no excretory system is present in either the Trichuroidea 

 or Dioctophymatoidea (Linstow's Pleuromyarii; Rau- 

 ther's Hologonia). In the related Dorylaimoidea ordi- 

 narily no excretory pore may be observed but a rudi- 

 mentary pore has been mentioned by some authors and 

 de Coninck (1931) illustrated a terminal excretory duct 

 connected with a ventral gland cell in Diphtherophora 

 vanoyei. A similar arrangement is indicated for the 

 Mermithoidea in which an excretory pore and terminal 

 excretory duct is commonly attributed to pre-parasitic 

 and young parasitic mermithids (Fig. 93). In adult 

 mermithids usually no pore is to be observed, but forms 

 in which the structure has persisted have been described 

 by Rauther (1909), and Steiner (1919). Corti (1902) 

 described in Hydromermis rivicola an excretory canal 

 in one lateral chord but no excretory pore was observed 

 and the structure was not illustrated. Hagmeir (1912) 

 described and figured the ventral gland devoid of any 

 terminal duct in adult Mermis brevis, and the writers 

 observed a similar structure in Hydromermis sp. 



The families Tripylidae and Mononchidae resemble 

 dorylaimoids in that the excretory system is usually in- 

 conspicuous or overlooked. Cobb (1918) established the 

 existence of an excretory pore in Mononchulus ventralis 

 and the writers have seen such in sections of Prionchulus 

 miisconim. As yet the internal connections of the excre- 

 tory tube have not been determined. 



The excretory system of plectids remains to be dis- 

 cussed. As in so many other characters, so here also, 

 the plectids show greater resemblance to the rhabditoids 

 than to any other phasmidians. The conception of the 

 excretory system of plectids has been confused consider- 

 ably by interpretations. The odd loop of the terminal 

 duct (Fig. 112 N) gave the genus its name. At the 

 level of this loop there are a large ventral gland cell 

 and two dorsal cells (Fig. 114 W). We have previously 

 (see Fig. 15 A) conceived the terminal duct as entering 

 the two subdorsal cells but this seems to be wrong; it 

 enters only the ventral cell. The only suggested function 

 of the other two cells is athrocytic. It should be noted 

 that AnaplectKH and Flectiis have no lateral canals though 

 they have a well developed termmal duct; whether or 

 not the duct itself has its own nucleus in addition to 

 the gland nucleus we cannot say. Anonchus mirabilis 

 provides another and even more interesting bit of evi- 

 dence as to the evolution of the excretory system for 

 in it one finds an inverted U-shaped system in the body 

 c Lvity and not in the lateral chords; in this instance 

 there is a distinct terminal duct, apparently with a sepa- 

 rate nucleus, and a large sinus cell from which two 

 apparently solid protoplasmic appendages extend pos- 



132 



