in some forms sueli as DesmvUiiinus this structure forms a sep- 

 arate and distinct organ which may be termed the ventricular 

 column (Figs. 82, 87J). Monhysterids (Figs. 82, 87A_-D) 

 have a more cylindrical esophagus, though never a distinct 

 linhomoeid bulb, and the ventricular column is never elon- 

 gated ; the posterior radial nuclei have the same odd type of 

 arrangement as linlionioeids but the radial musculature is of a 

 dispersed type throughout, the esophageal lining without thick- 

 enings, the lumen very simply triradiate and the esophago- 

 intestinal valve less elongate but otherwise similar to that of 

 TerscheUingUi (Fig. S7G-I) ; the latter structure contains 19 

 to 23 nuclei. Siphonolaims have a very short corpus, an elon- 

 gate isthmus, a short glandular bulbar region and a short 

 esophago-intestinal valve containing six nuclei. The nuclei of 

 the bulbar region are as in linhomoeids and monhysterids but 

 only three marginal and 18 radial nuclei are present in Sipho- 

 nolamiis conicus. Monhysteroids are peculiar in having very 

 minute marginal nuclei (Fig. 87A). 



In the suborder Monhysterina one first encounters paired 

 pigment spots in the subdorsal or dorsolateral regions of the 

 procorpus in a few genera of the Camacolaimidae (Onchinm 

 ocellatum) and A.xonolaimidae {Araeo!aimus). These peculiar 

 structures are situated in the dorsal parts of the subventral 

 sectors (dorsolaterally ) or the lateral parts of the dorsal sector 

 (subdorsally) ; there is, in the first mentioned genus, a pair 

 of acorn like pigment masses each provided with a hyaline 

 lens. While these are termed ocelli, no one has thus far con- 

 nected them with sensory nerves. In MonhysUra pahiilicoln 

 similar ocelli are situated in the body cavity dorsal to the 

 esophagus. 



CHROMADORIKA. — lu the subordcr Chromadorina the eso- 

 phago-intestinal valve is usually short though sometimes 

 elongate but never dorso-ventrally tiattened ; it always retains 

 its triradiate character. None of the representatives of this 

 group preserve semblance to rhabditoid or plectoid esophagi. 



In the Chromadoroidea the esophagus consists essentially 

 of a cylindrical corpus and a bulbar region (Fig. 91); the 

 esophageal lumen is triradiate, the lining unmodified, so far 

 as known, though the radial uruscles are definitely concentered. 

 Members of the Chromadoridae such as Cliroiiiaihna and Etlimo- 

 Jaimus revaliensis have a very short esophago-intestinal valve 

 containing 12 or 1.3 nuclei (Figs. 86, 88); 12 marginal and 30 

 radial nuclei are present in the esophagus, the posterior nuclei 

 of the bulbar region being arranged in tw^o typical groups of 

 three. In Microlaimns dentatum the esophago intestinal valve 

 containing 11 nuclei is elongate reminding one of Tersehel- 

 liii(/i(i, but differs from that form in being triradiate (Fig. 

 8<) B-C). Chromadoroids show no tendencies toward diminu- 

 tion in nuclear numbers such as was noted in monhysteroids 

 but, rather the opposite. Several "additional nuclei" make 

 their first appearance in this group; the arrangement and 

 positi(m of these nuclei (s, c, and x) are characteristic of both 

 chromadoroids and desmodoroids (Fig. 00). 



f'yatholaims generally have a much elongated trijiartite bul- 

 bar region or a cylindrical esophagus. In representatives of the 

 former type {Paracanihonclnix coccti.i) the lumen of the esoph- 

 agus may be slightly enlarged marginally (Fig. 84 N-P). 

 (jhoanolaims and tripyloids, on the contrary, have a typical 

 triradiate lumen with long rays as in monhysterids rather 

 than the short rays and minute lumen typical of the Chroma- 

 dorina. All of these foims have a rather large and well de- 

 veloped but short esophago-intestinal valve. 



Desmodoroids have the same general esophageal organiza- 

 tion and the same general pattern of nuclear distribution 

 (Fig. 89) as do chromadoroids but the esophageal lining may 

 have thickened cutieular attachment points (Mclaclirnmadoru 

 oiiiixoides) . 



The so-called "multiple huDi'' of chromadoroids and des- 

 modoroids deserves special ]i]cnti(]n. In both superfamilies one 

 may trace series of foruis from a subspheroid bulb to a sub 

 cylindroid tripartite bulb thence to a cylindrical esophagus. 

 The apparent sub-division of the buUiar region in forms such 

 as Monopoxlliia lu-.rtilata and EUiniolaimii.i revaliensis (Fig. 91) 

 into two jiarts is due to a particular arrrangement of the mus- 

 culature and glandular tissues and a break in the thickness of 

 the esophageal lining at the points where one muscle ceases 

 and another begins. This break indicates the separation of 

 radial subgroui)S of muscles containing nuclei r.n-.ii and 

 r:ii-:»i resi)ectively and is essential to the function of this type 

 of bulb. The musculature containing the radial nuclei rr,.j,i is 

 in the anterior part of the trip.-irtite bulb ami tlir corresjiond- 

 ing muscles are a separate functional unit. 



I'iguK'nt spots in the anterior part of the corpus are com 

 monly found in nu'inbers of the (^hromadoridae .'ind like those 

 previously nirnticmi'd in the Ciini.-icohi imid.-io and Axnnolainii 



dae they are situated in the subdorsal marginal regions of 

 the esophagus but in this case the pigment is diffuse rather 

 than concentrated aud is not provided with a lens. It seems 

 proper to designate ihese as mere pigment spots while reserv- 

 ing the term ocelli for concentrated pigment bodies accom- 

 panied by lenses. De Man (1889) described true ocelli situated 

 dorsal to the esojdiagus in the body cavity of Cyathtilaimus 

 demani (Syn. Cyalholainuis ocellatiis of de Man). 



The esophagi of desmoscolecoids have not as yet been ade- 

 quately studied. The esophagus is grossly rather cylindroid 

 but narrow, the three esophageal glands projecting posteriorly 

 indicating a leduction in the musculature of the bulbar region. 

 Such forms (Fig. 17) have well developed, brilliantly col- 

 ored pigment bodies dorsal to the base of the esophagus. 



Enopuda. — The esophagi of representatives of this order 

 commonly (always?) have five or more uninucleate or multi- 

 nucleate esophageal glands. The esophagus usually has an 

 elongate muscular anterior part followed by an elongate 

 glandular posterior part, such divisions resembling those of 

 spiruroids and filarioids. The location of the esophageal gland 

 orifices varies widely in the group. 



ENOPLiN.i. — Esophagi of representatives of this sub-order 

 have been studied by Marion (1870), de Man (1886, 

 1904), Jcigerskiold (1901), Turk (1903), Rauther (1907) and 

 the writers (1937). In general we find tw-o types of esophagi 

 in this group : the first type in which the esophageal glands have 

 orifices rather near their nuclei, that is, in the posterior glandu- 

 lar part of the esophagus (such forms are included in the super- 

 family Tripyloidea) ; and the second type, in which the sub- 

 ventral esophageal glands open anteriorly either near the base 

 of the stomatal region or in subventral teeth (such forms may 

 occur in either of the superfamilies Enoploidea or Tripvloi- 

 dea ) . 



In the Tripyloidea the esophagus either is cylindrical (Prion- 

 chulus, Tripyla) or consists of an elongated narrow corpus 

 and a slightly wider elongate glandular region ( Alaimiis) ; 

 in all such forms studied there are five uninucleate esophageal 

 glands, one dorsal and four subventral (Fig. 91). Mononchs 

 such as Prionchuliis muscornm have concentered radial muscles 

 and well developed cutieular attachment points (Fig. 92) ; the 

 esophago intestinal valve which is triradiate and quite massive 

 (Fig. 92M), contains 22 nuclei in P. muscorum. A total of 36 

 radial and nine marginal nuclei have been observed, the radials 

 (12 in procorpus, 12 in metacorpus and 12 in glandular region) 

 are arranged in sets of six, indicating that even those of the 

 posterior gioup act as a single unit rather than as two units 

 as in rliabditids, plectids and chromadorids. Nuclear distri- 

 bution (Fig. 90) indicates quite definitely that the glandular 

 region of the esophagus of Prio^ieliuliis as well as other tripy- 

 loids, enoploids and dorylaimoids is homologous to the bulbar 

 region of the orders Rhabditida and Chroniadorida rather than 

 the glandular region of spiruroids since it does not contain the 

 radial nuclei characteristic of the metacorpus (total nunilier 

 of radials 18 in spiruroids). The five esophageal gland nu- 

 clei are subequal in size and each of the accompanying glands 

 opens nearly directly into the esophageal lumen (Fig. 94D). 



In Tripyla papillata and Trilohns lemgiis the musculature is 

 dispersed, no cutieular attachments are present and the esoph- 

 ago intestinal valve is quite massive, consisting of an external 

 part containing six or seven large nuclei and an internal part 

 containing up to 100 nuclei (Fig. 94 E-L). This peculiar 

 structure, sometimes termed a pseudo-bulb, or bulb, is com 

 monly thought to be a part of the esophagus irroper but this 

 does not appear to be the case. It is a further development 

 of the type of valve found in Prionchuliis. The five esophageal 

 glands are similar to those of the latter genus except that the 

 dorsal and the fii'st pair of subventral esophageal glands extend 

 to the base of the stomatal region where they open.* Alaimiis 

 is similar to Tripyla except that the radial muscles are con- 

 crnlered ; the triradiate esophago-intestinal valve is quite small 

 and inconspicuous, and the subventral glands do not extend 

 l>eyond the enlarged glanil\ilar region. 



In the sujierfamily Enoploidea the gross form of the esopha- 

 gus varies considerably, there being types with a cylindrical 

 esoiihagns, types in which the narrow corjnis is followed by a 

 gradually I'xpanding elongate glandular region (conoid") and 

 t.vpes in which the coipus is slightly narrower and set off in- 

 ternally from an elong.ate cylindrical bulbar region. Due to 



*On the bnsis of esopliageal structure the current concept of the supei-- 

 f.'ii?iily Tripyloideft must tie revised, preferahly to include the Tronidae. 

 Tlie i)osition of the gliind orifices as previously stated for Ti'ipi/lii (PP- 

 1 (i and .'J2) is not in accordance with present tindiiif^s. Temporarily, 

 the alisence of cutieular duplication at the he.-id may he considered the 

 limiting character of the Tripyloidea (includinir the Tronidae) as op- 

 I)osed to the J)resence of cutieular duidication in the Enoploidea. Tjater 

 we hope to lie in a position In adrl further characters to substantiate 

 this revision. 



86 



