with that of dorylaiiiiids hut only three large esophageal glands 

 have been observed ; iiresumably both of the first pair of 

 subventral glands in this instance are small. Triploncliium 

 of the Diphtherophoridae has very feebly developed, if any, 

 thickened cutieular attachment points of the esophageal lining, 

 and the dorsal and first pair of subventral gland nuclei (sit- 

 uated at the same level) is only slightly smaller than the 

 posterior subventral pair (Pig. 94 JJKK). 



The esophagi of the mermithoids have been studied by Eau- 

 ther (1906), Hagmeier (1912), G. W. Mijller (19.31), Christie 

 (1936) and the writers (1935, 1937) as ivell as many others 

 who have added scattered bits of information. The peculiarity 

 of the mermithoid esophagus is its relatively great length and 

 tenuousness. In the adult stage, which does not feed, the 

 greater part of the esophagus posterior to the nerve ring ap- 

 pears as a slender tube covered with a bit of ])rotoplasm to 

 which various types of cells are attached at intervals. The 

 esophageal musculature appears to be entirel.v degenerate. 

 One must turn to the larval stages of mermithids for an un- 

 derstanding of these structures. 



The preparasitic larva has an esophagus consisting of a 

 short anterior part terminated by a muscular swelling and 

 followed by an elongate narrow posterior part with which 

 glands are associated. There are three unicellular elon- 

 gate esophageal glands extending posteriorly into the body 

 cavity from the base of the anterior (non-glandular) portion, 

 the dorsal being considerably larger than the subventrals; 

 these primary glanclst (Fig. 93) become atrophied after the 

 entrance of the larva into its host. In addition there is a 

 double series of large cells (stichocytes) attached to and co- 

 extensive with the posterior part of the esophagus. These 

 cell.s are secondary esophageal glands, probably representing a 

 reduplication of the posterior pair of subventral esophageal 

 glands of dorylaims and enoplids. In the parasitic stage these 

 glands become much enlarged (Fig. 93) and later they too 

 atrophy as the larva approaches adulthood. The lining of the 

 esophagus of mermithids is rather clearly triradiate in the 

 preparasitic larva, becoming subtriangular in later stages un- 

 til finally the basic triradiate character is scarcely discernible 

 (Fig. 96A-E). In Aflamcrmis decatulata 48 large nuclei cor- 

 responding to the marginals and radials are present, most 

 of them arranged with little indication of pattern, and there 

 is even less indication of muscular fibers in the parasitic lar- 

 vae (Fig. 96). There arc 27 such nuclei anterior to the ori- 

 fices of the primary glands indicating that this region corre- 

 sponds to the corju'.s while there are 21 in the posterior part, 

 indicating that it corresponds approximately to the bulbar 

 region. These nuclei are situated within the wall of the 

 esophagus proper. Each of the glands of both types has an 

 orifice not distant from its nucleus. There is one peculiarity 

 of the esophagus which does not seem reconciled with the tre- 

 mendous esophageal gland development in the parasitic stage, 

 namelj', that the lining disappears posterior to the orifice of 

 the last stichocyte and the lumen does not connect with the 

 degenerate intestine. The stichocytes are fpiite obviously 

 functional and it is difficult to believe that fluid food is not 

 drawn in through tlie esophagus but if so, we do not know 

 its destination. The number of stichocytes varies from four 

 to 16 or possibly more, according to the particular form. 



The peculiar esophagus of trichuroids has long been a sub- 

 ,iect for study. Eberth (1860, 1863), Leuckart (1S66), Eau- 

 ther (1918), G. W. Miiller (1929), Christenson (193.5) and 

 the writers (1929, 193.'>, 1937) have investigated various forms 

 of this group. Ward (1917) proposed a separate suborder 

 for trichuroids and mermithoids (Trichosyringata) based on 

 the peculiarity of the esophagus. The esophagi of mermithoids 

 and trichuroids are similar but not fundamentally different 

 from other nematodes. Ward stated "A type of radically 

 different character is the cai)ill:iry esophagus ... It consists 

 of a row of cells, pierced throughout its entire length by a 

 delicate tube." The cells of which he speaks are stichocytes 

 or esophageal glands attached to but not "pierced by" the 

 esophagus proper which is to a greater or lesser degree em- 

 bedded in these cells. As in mermithids, the wall of the 

 esophagus contains its own nuclei. Much discussion has cen- 

 tered around the significance ;ind nature of the structures, but 

 since the points now are clear, further discus.sion seems un 

 necessary. 



The anterior part of the esophagus of Trirhiiris iivis is nar- 

 row and muscular, terminated by an elong.-ited swelling; the 

 lumen is trir.-idiate, the lining thick but without attachment 

 points. Within this region, besides nerve cells, one group of 

 three marginal nuclei and two groups of six distinct radial 

 nuclei are present. On this basis one might presume it to be 

 the iirocorpus but within the terminal swelling a set of three 



large nuclei of esophageal glands is present (Fig. 91 & 961). 

 These glands, whose orifices are posterior to the nerve ring, 

 doubtless correspond to the primary glands of mermithids. 

 The posterior part of the esophagus is cjuite narrow and em- 

 bedded in a single series of large cells (cell body ' 'zellkorper" 

 of authors). The narrow "tube" or esophagus proper is 

 triradiate to hexaradiate and has its own wall containing 

 radial nuclei as well as nerve cells occurring at intervals. Con 

 trary to general supposition, this wall contains well developed 

 radial muscle fibers (Fig. 96M). The large cells in which 

 it is embedded are esophageal glands, each having a separate 

 orifice reached or formed by a tube through the esophageal 

 wall. This being the case, there is no fundamental difference 

 from other nematodes in which the esophageal glands may 

 come to lie outside the esophageal contour (Contracaeciim, 

 Aphelencluis, Onchium) . Because of the fact that in larval 

 trichuroids the stichocytes are more or less alternatel.v paired 

 and the orifices in the adult tend to alternate it seems reason- 

 able to assume that the single row stichosome of Trichurix 

 is a later evolutionary development from a double row of 

 stichocytes such as is found in mermithoids. This view is sup- 

 ported by the illustrations of .lanicki and Rosin (1930) of the 

 esophageal region of Cj/stoopsi.i which shows two rows of 

 stichocytes. The number of stichocytes seems to be variable 

 to some extent within a given species of trichuroid. 



At the end of the esophagus, unlike mermithoids, we find a 

 direct connection of the esophagus with the functional intestine 

 formed by a dorsoventrally flattened esophago-intestinal valve 

 such as is present in dorylainioids. Two large cells (Fig. 960) 

 described as glands with direct openings into the esophageal 

 lumen, by Eberth (1860, 1863), are attached to the esophagus 

 at its base. Neither Eauther (1918) nor the writers were 

 able to distinguish any protoplasmic connection of these cells 

 with the esophageal lining or any tubules in the cytoplasm 

 of these cells. It now seems possible that these cells are en- 

 larged mesenterial cells, homologous to the series of smaller 

 cells supporting and covering the esophagus and stichosome 

 (p. 45). 



DiocTOPHYMATiN.\, — The esophagus of the suborder Diocto- 

 phymatina has received little attention since the first re- 

 port of Schneider (1866) that the walls of the cylindrical 

 esophagus of such forms contain numerous longitudinal 

 "tubes." No additional information was added until the 

 subject was recently reopened by the writers (1937). The 

 esophageal lining is simple, the lumen triradiate and the well 

 developed musculature dispersed in representatives of this 

 group. There is no division, either grossly or internally, into 

 anterior and posterior parts. The three massive esophageal 

 glands have their orifices at the anterior end of the esophagus 

 and begin branching dichofomously near the level of the 

 nerve ring; glandular tissue is thereafter interspersed between 

 the radial fibers to the base of the esoidiagus. It appears that 

 there are 36 radial and nine marginal (or possibly 121 nuclei 

 in the esophagus. The radials are arranged in suligroups of 

 three, one near the center of each sector. The esophago-in- 

 testinal valve is triradiate. 



The highly remarkable esophageal glands deserve special 

 note. Each has a short terminal duct lined with cuticle, fol- 

 lowed by a short, thick walled primiiry tubule which bifurcates 

 into secondary tubules. In Sobnlipliiime haturini the second- 

 ary tubules appear to be lined with cilia (Fig. 95FF). Here 

 and in EustronQi/lides these secondary tubules branch dicho- 

 fomously, time after time, throughout the length of the esoph- 

 agus and come to nearly fill the non-muscular part of their 

 sectors (Fig. 95CC-DD) but do not enter other sectors. The 

 marginal tubules end blindl.v (Fig. 97C) and their position is 

 taken by others formed by the branching of the more centrally 

 located tubules. In Dioctopliipna renale the .same condition 

 exists with the exception that the secondary tubules of the 

 dorsal gland do not undergo further branching (Fig. 1I5BB) 

 and tubules from the subventral glands take ;i marginal jiosi- 

 tion in the dorsal sector (Fig. 97B). In all cases we find 

 dense glandular ])rotoi)lasm containing numerous gland nuclei 

 (Fig. 95CC-DI)) surrounding the tubules. There are literally 

 hundreds of such nuclei. Whether the subventral glands cor- 

 respond only to the anterior pair of subventral esophageal 

 glanils or to both anterior and posterior jiairs of subventral 

 glands of enoplids is uncertain. 



The dioctoiihymatid esophagus resembles the enoplid esopha- 

 gus in the position <if the orifices of the esophageal glands and 

 .•ilso resembles to some extent that of the leptosomatids in the 

 multinucleate condition of the gl;uids. However, the jieculiar 

 dichotomous branching of the tubules has its only parallel in 

 the branched dorsal gland of Dorylaimus. 



92 



