Peripheral nervous system. The peripheral nervous 

 system of nematodes consists of the somatic nerves, the 

 cephalic papillary nerves, aynphidial nerves, genital papil- 

 lae, cephalic papillae, amphids, deirids and postdeirids. 



Somatic Nerves. Those nerves which extend through 

 the length of the body in the hypodermis are called somatic 

 nerves. These include the dorsal nerve which originates at 

 the posterior surface of the nerve ring with the dorsal 

 ganglion and extends posteriad in the dorsal chord to 

 the postanal region where it bifurcates, both branches 

 extending through the hypodermis to the lumbar ganglia 

 forming the dorsolateral lumbar commissures. 

 Throughout its length no ganglia have been ob- 

 served. It connects directly with innervation processes 

 from the somatic muscles and is considered a motor nerve. 



Laterodorsal somatic nerves originate at the dorso- 

 lateral side of the nerve ring at which point each contains 

 one bipolar neurone. Thereafter, they extend through 

 the hypodermis to the laterodorsal (submedian) lines 

 where they assume a longitudinal posteriad course. 



Lateroventral somatic nerves arise from the lateroven- 

 tral part of the nerve ring and pass through the ventral 

 ganglia where each has a bipolar neurone. They then 

 leave the ventral chord with the major lateroventral 

 commissures and reach the lateroventral (submedian) 

 lines and extend posteriad like the laterodorsals. Neither 

 of these paired "submedian" nerves has any ganglia in 

 its course and like the dorsal nerve the submedians are 

 considered motor nerves since they connect with in- 

 nervation processes of the somatic musculature. 



The Ventral nerve has already been described as part 

 of the central nervous system and though it undoubtedly 

 contains associational centers, it also acts as a motor nerve 

 since it innervates the muscle cells in the subventi-al 

 muscle sectors. 



Dnrsoventral co7nmissures have previously been men- 

 tioned. These occur at intervals throughout the body 

 and with one exception, the anterior dorsoventral com- 

 missures, they are unpaired and are supposed to co- 

 ordinate the activity of the somatic muscles. Goldschmidt 

 (1908) was of the opinion that the "submedian" somatic 

 nerves were also connected with the ventral nerve by 

 these commissures but this has not been adequately 

 demonstrated. 



Ventrolateral nerves originate from the internolateral 

 ganglia, the anterior and the medial externolateral gang- 

 lia ; the fibers from these ganglia come together posteriad 

 and the nerves so formed extend posteriorly at the side 

 of the excretory canal. Further ganglia have not been 

 observed in their course until they reach the posterior 

 extremity. In the anal region of the female each ventro- 

 lateral nerve contains a group of nerve cells called 

 the lumbar ganglion. At approximately the same level 

 the ano-lumbar commissure connects it with the ventral 

 nei"ve. Paired lateral nerves which continue posteriad 

 from these ganglia are called the lateral caudal nerves. 

 They innervate the phasmids in the female. In the male 

 the ventrolateral nerve (also failed the bursal nerve) 

 innervates the genital papillae and paired genito-papillary 

 commissures connect it with the ventral nerve. Postanal 

 genital papillae are innervated by processes from the 

 enlarged lumbar ganglion and branches of the lateral 

 caudal nerves. The lateroventral somatic nerve is thus 

 seen to be at least partly a sensory nerve. 



Dorsolateral nerves have been described by Hesse 

 (1892), Brandes (1899) and Voltzenlogel (1902). Gold- 

 schmidt (1908) apparently overlooked them; they might 

 correspond to the short processes extending posteriad 

 from the anterior externolateral ganglia. They unite 

 posteriad with the ventrolateral nerve in the anal region. 



Cephalic papillary nerves and papillae. There are six 

 anterior papillary nerves arising from the anterior sur- 

 face of the nerve ring and extending to the anterior 

 extremity; unlike the somatic nerves, the papillary nerves 

 go through the body cavity, being applied closely to the 

 external surface of the esophagus. Each of these nei'ves 

 contains a ganglion (cephalic papillary) of bipolar nerve 

 cells at the anterior surface of the nerve ring. The 

 sensory endings of the nerves include the cephalic papil- 

 lae. Each subdorsal and subventral cephalic papillary 

 nerve terminates anteriad in a large pair of partially 

 fused papillae (dorsodorsal and laterodorsal or ventro- 

 ventral and lateroventral) of the external circle, and a 

 small rudimentary papilla (internodorsal or internoven- 

 tral) of the internal circle. The lateral papillary nerves 



each terminate in one large papilla of the external circle 

 (ventrolateral) and a rudimentary papilla of the internal 

 circle (internolateral). 



Aniphidial nerves and amphids. Like the cephalic 

 papillary nerves, the amphidial nerves each innervate 

 a cephalic sensory organ but unlike the papillary nerves 

 their connection with the nerve ring is indirect. The 

 nerve cells are situated in the amphidial ganglia which 

 lie posterior to the nerve ring, and their axones pass 

 into the major lateroventral commissures to the ventral 

 nerve trunks before reaching the nerve ring. Anteriorly 

 each amphidial nerve enters an amphidial gland and its 

 processes break up in an elongate sac, amphidial pouch; 

 the sensory elements which represent the specialized ends 

 of individual neurones are called terminals and the group 

 of elements is called a sensilla. From the pouch, anteriad, 

 there is a short amphidial duct which opens to the outside 

 at the ai.\phidial pore. 



Deirids. These are paired papillae in the cervical 

 region commonly called cervical papillae. Each is innerv- 

 ated by a branch of the nerve trunk which connects 

 the medial externolateral ganglia with the nerve ring; 

 the sensory cell of each deirid lies in that ganglion. 



Postdeirids. These are paired and asymmetrically placed 

 papillae first seen by Hesse (1892), in the mid-region of 

 the body. Each is innervated by a single nerve fiber 

 connected with a sensory neurone in the lateral chord. 

 The axone passes through the hypodermis to the ventral 

 nerve. 



Genital papillae and Connections. Each preanal genital 

 papilla sends a nerve fiber through the hypodermis to 

 the lateral chord where it enlarges to form a bipolar 

 neurone the axone of which joins the ventrolateral somatic 

 nerve and reaches the ventral nerve by way of a genito- 

 papillary commissure. In addition there is a medioventral 

 preanal papilla which, according to Voltzenlogel (1902) 

 is innervated by four bipolar neurones connected di- 

 rectly with the posterior end of the ventral nerve. (Fig. 

 128 C). Posterior to the anus the genital papillae are 

 innervated by processes of the lumbar ganglia. Of 

 these, the first pair is double and has two nerve fibers. 



Phasmids are known to occur in both sexes of Ascaris 

 and to be innervated by processes of the lateral caudal 

 nerves but no further details have "been obtained. 



Topographic Anatomy of the Nervous System of Species 

 Other Than Ascaris 



The nervous systems of only a few other nematodes 

 have been studied, namely: Siphonolaimus weismanni by 

 zur Strassen (1904), Ancylostoma duodenale by Looss 

 (1905), He.ramermis albicans (syn. Mermis albicans) by 

 Rauther (1906), Oxyuris equi by Martini (1916), Rhab- 

 ditis .ftrongyloides by Chitwood (1930), Camallanus spp. 

 and Cucullanus hcterochrous by Tornquist (1931), Ceph- 

 alobellus papilliger by Chitwood and Chitwood (1933) 

 and Rhabditis terricola by Chitwood and Wehr (1934). 

 In preparing this volume we have made a point of 

 studying two additional species, Spironoura affine and 

 Oesophagostomum dentatum. Restudy of Rhabditis 

 strongyloides has shown that trust was misplaced in 

 the use of methylene blue as an intravitam stain and the 

 publication in which it was described (Chitwood, 1930) 

 contains so many gross errors that it should be ignored. 

 The correct form of the nervous system of Rhabditis is 

 shown in Fig. 8. The general features of the nervous 

 system in all the forms studied is very similar even though 

 they represent considerably diverse groups. 



Central nervous system. Differences in the central 

 nervous system lie chiefly in the degree of subdivision 

 of the lateral ganglia, the form of the ventral ganglia 

 and degree of fusion of the ventral nerves. 



In Siphonolaimus weismanni (Fig. 129 I) the ventral 

 nerves are paired as far as they have been traced but 

 this tracing did not extend so far as the retrovesicular 

 ganglion. In Ancylostoma duodeyiale, Oesophagosfomum 

 dentatum, Spironoura affine, Cephalobellus papilliger, 

 and Rhabditis terricola they are fused in the retrovesicular 

 ganglion and thereafter are apparently single but, con- 

 sidering the minuteness of the left fiber group, doubleness 

 of the ventral nerve might be overlooked. In Oxyuris equi 

 (Fig. 129 C) Martini found the ventral nerves paired 

 to the posterior side of the vulva which happens to be 

 situated distinctly pre-equatorial in this species. In the 

 other species the ventral nerve passes to the right side 

 of the vulva. Both Martini (1916) and Chitwood and 



162 



