IV. Adenophori. Small high lateral chords; ventral 

 pore present, connected with a ventral cervical gland ; 

 two spicules; herein the free-living nematodes should 

 be placed. (Myenchus, Myoryctes, Hhabditis, Cephalobus) . 



The Secernentes by definition correspond to the Phas- 

 midia and the examples include representatives of four 

 out of five of the major phasmidian groups, i. e., 

 Strongylina, Ascaridina, Caniallanina and Spirurina. The 

 group Resorbentes was less fortunately constituted, since 

 it was primarily based upon a supposed method of feeding 

 which the author attempted to correlate with anatomy. 

 On the basis of present day information all representa- 

 tives except Dioctophynia would be placed in the Secern- 

 entes. The exceptional genus might be placed with the 

 Pleuromyarii (on the basis of one spicule) or the 

 Adenophori (on the basis of chords). From the stand- 

 point of excretory system, or lack of it, the Pleuromyarii 

 must be considered synonymous with the Adenophori. 

 Steiner (1919) criticised von Linstow rather severely 

 for having put forward such a classification because it 

 was well known that Rhabditis and Cephalobus had lateral 

 excretory canals. The evidence today shows that Linstow 

 was in error as to all of the examples af the Adenophori 

 which he listed. However, it should be recognized that 

 Linstow was right in his fundamental conception. Most 

 free-living nemas differ from typical parasitic nomas 

 in that they have no lateral excretory canals. Linstow 

 had little choice of example since he was discussing the 

 parasitic nemas and covered free-living forms only to 

 the extent that they occurred as parasites. 



Today we find ourselves following very closely the 

 definitions Secernentes and Adenophori as given by von 

 Linstow though ignoring his examples. The Secernentes 

 are absolutely equivalent to the ±^hasmidia while the 

 Adenophori correspond to the Aphasmidia. It is of 

 further interest to note that the presence of lateral 

 canals is always evidenced by a cuticularly lined terminal 

 duct or excretory vesicle; furthermore, the reverse is 

 also true with only two exceptional instances (Plectidae 

 and larval mermithids). In all instances carefully in- 

 vestigated in recent years, the tubular excretory system 

 occurring in the Phasmidia has been found to consist of 

 not less than two cells, one or more forming the cuticul- 

 arly lined terminal duct and one or more forming the 

 lateral canals and glandular tissue. The Aphasmidian 

 unicellular gland lacks the cuticular lining of the termi- 

 nal duct and consists of a single gland cell with no canals. 

 We may conceive of this system as the homologue not of 

 the entire Phasmidian system but only of the ectodermal 

 part, i. e., the terminal duct cell. 



Secernentes (Phasmidia) 



In the first group, there are four chief modifications 

 of the excretory system (Fig. 9, p. 11), namely (1) the 

 oxyuroid or simple H system (oxyuroids, some ascaridoids, 

 some scattered members of the Spirurina) ; (2) the 

 rhabditoid system, a combination of the H type with 

 two subventral glands (known m some rhabditids and 

 strongylins) ; (3) the ascaridid inverted U-system, char- 

 acteristic of ascaridids but occurring also in most mem- 

 bers of the Spirurina and some free-living forms 

 (Panagrolaimus) ; (4) the asymmetric system, known 

 only in Anisakinae and Tylenchoidea. 



Critical study indicates types (3) and (4) have ap- 

 peared more than once in the general evolution and 

 both types may be considered as ordinary variations of 

 type (1). Type (2) is known only in one parasitic group, 

 the Strongylina and in some representatives of one 

 free-living group, the Rhabditidae.. Normal progressive 

 evolution would account for the origin of the rhabditoid 

 system from the oxyuroid system. 



(1) Simple H System. This type, commonly spoken 

 of as the oxyuroid system, is by no means limited to 

 oxyuroids. There are several variants of the system, 

 chiefly dependent upon the form of the terminal excre- 

 tory duct. 



(a) Terminal duct long and tubular. 



(b) Terminal duct greatly shortened, tout not vesicle- 

 like. 



(c) Terminal duct elongate, vesiculate. 



(d) Terminal duct a very short vesicle. 



(la) Presumably, the elongate, cuticularly lined termi- 

 nal duct is the more primitive type. In such a system 

 one finds at least one, sometimes two nuclei attached to 

 the terminal duct and one large sinus nucleus. Long 

 anterior canals are known only in free-living nemas such 

 as Rhabditis dolichura and Cheilohus schneideri (Fig. 

 112A). Excretory systems of such forms have been 

 studied by Butschli (1873), Jagerskiold (1909), Magath 

 (1919) and Tornquist (1931). Undoubtedly this type 

 of system is more widespread In the Rhabditoidea than 

 is known; it is very closely approached in ascaridids. 

 Tornquist found representatives of both the 

 Camallanidae and CucuUanidae with H type systems 

 and both H and inverted U forms existing within the two 

 genera Procamallanus and Camallanus, the H type being 

 confined to camallanids of fish. There are really two 

 quite distinct forms for this system. In Camallanus (Fig. 

 112 F-G) one finds two nuclei within the wall of the 

 terminal duct, one nucleus near the pore and one near 

 the anterior surface of the sinus. In this case the terminal 

 duct connects with the sinus near the left lateral chord 

 and there is a large sinus nucleus on the left side (Fig. 

 114 CC). The lateral canals begin as thick walled tubes, 

 sometimes with indistinct, questionable, tributary tutoules; 

 thereafter the canals become smaller and they never have 

 a thick lining nor have nuclei been observed in their 

 walls. This, then, is a three nucleate or three celled 

 system. 



In Cucullaniis, according to Tornquist, (1931) some- 

 times the terminal duct is dilated like a bladder near the 

 pore (like b or d). There is no distinctive sinus nucleus 

 but there are many similar nuclei within the walls of 

 the posterior lateral canals which should probably be 

 interpreted as multiples of the original sinus nucleus 

 (Fig. 112 E). The walls of the lateral canals are thick 

 throughout their length but are particularly massive in 

 the cervical region and taper posteriad (Fig. 114 L). 

 Distinct branching tubules penetrate the wall of each 

 canal, these being best developed in the cervical region 

 (Fig. 114 M); the tubules do not leave the canal tissue. 

 Tornquist found such tubules arising more or less sym- 

 metrically in fours, two dorsolaterally and two ventro- 

 laterally from the canal axis, while the writers have 

 found six series of tubules more common, there being 

 two lateral ones in addition to those previously men- 

 tioned. 



The multinucleate character of the cucullanid excretory 

 system was first noted by Jagerskiold who considered 

 the whole system as representing a polynucleate cell. 

 Tornquist and the writers have confirmed Jagerskiold 

 in not being able to find cell walls- However, we may 

 well question our interpretation of this case until further 

 information is obtained relative to the occurrence of 

 nuclei in lateral canals. Such findings are becoming 

 common. 



(lb) The shortened terminal duct type, as exemplified 

 by Heierakis galliyiae (Fig. 112 B), is very similar to 

 (la) and probably should be considered a modification 

 thereof. The observations of Wagener (1857), Eberth 

 (1860) and Schneider (1860) have previously been men- 

 tioned. More recently Chitwood (1931) and Baker 

 (1936) have restudied this foi-m. The excretory orifice 

 is guarded anteriorly by a lip cell (Fig. 113 RR) formed 

 from the anterior side of the terminal duct. Thence 

 internally the terminal duct is wide, irregular until it 

 merges with the excretory sinus. On the lower left hand 

 side a small nucleus is present in the terminal duct wall 

 (Fig. 113 JJ). The only means of distinguishing sinus 

 and duct is through the cuticular lining of the duct. 

 There is another nucleus on the ventral side associated 

 with the sinus and terminal duct but apparently exterior 

 to their walls (Fig. 113 KK) ; one often sees fibrous 

 tissue around the duct and near this nucleus, and it 

 seems possible that the nucleus and fibers represent a 

 sphincter muscle of the sinus and terminal duct. The 

 sinus nucleus itself is situated medially and is not es- 

 pecially large in Heterakis (Fig. 113 LL). No additional 

 nuclei have been observed in the lateral canals. The 

 heterakid system, therefoi-e, seems to consist of not 

 less than three nuclei or cells, two belonging to the 

 duct and one to the sinus and canal system. 



127 



