CHAPTER XI 



NERVOUS SYSTEM 



B. G. CHITWOOD and M. B. CHITWOOD 



Historical 



Otto (1816) is credited with the discovery of the chain 

 of gano-jia in the ventral cliord which we have since 

 come to recognize as the ventral nerve. This author 

 examined the two large ascarids, Ascaris bimbricoides 

 and Painscdiis eqiwrntit. Not long thereafter Owen 

 (1836-39) observed the ventral nerve and preanal gang- 

 lion in oioctophyina renale. Siebold (1848) reexamined 

 D. renale and was able to confirm the existence of a 

 ventral nerve but he did not see the preanal ganglion; 

 he also described fibers from the ventral nerve to the 

 somatic musculature. At about the same time Blanchard 

 (1847) studying various ascaridids and filarioids ascribed 

 a nervous function to the dorsal and ventral lines 

 (chords) and described two cell groups on each side of 

 the esophagus; these latter have sin;e been identified as 

 the paired lateral and ventral cephalic ganglia. 



Meissner (1853) working on Hexiimeynii^ cilhicans de- 

 scribed the nervous system in great detail and, consider- 

 ing his pioneer position, in a comprehensive and credit- 

 able manner. Briefly, he characterized the nervous 

 system of this species as follows: 



There i's o central nervous system consisting of a 

 fibrous ring around the esophagus and connecting four 

 subinecHan anterior ganglia, tivo lateral ganglia and two 

 posterior ventral ganglia (He termed this group of struc- 

 tures the brain) and three posterior ganglia, at the tail. 

 The lateral and anterior subnicdian ganglia supj)l!j the 

 six anterior nerves to the six cephalic papillae (Now 

 recognized as the amphids and various cephalic papillary 

 groups rather than individual papillae). Posteriorly 

 there are four longitudinal nerves, a dorsal, two latero- 

 ventral, and one ventral. Of these the dorsal originates 

 directly from the fibrous ring while the other three 

 originate as tivo subventral nerve trunks which unite 

 posteriorly as the ventral nerve from which the latero- 

 ventrats branch off. Three of thc^c longitudinal nerves 

 are connected posteriorly uuth ganglia. The somatic 

 musculature is connected with the longitudinal nerves, 

 the nerve processes and the muscle cells merging so that 

 one cannot say where one begins and the other ends. 



So far as this description goes it is reasonably accurate 

 but, as we shall see later, it received a great deal of 

 criticism. 



Wedl (1855) saw the nerve ring in various parasitic 

 nemas but mistook the sarcoplasmic part of the muscle 

 cells for ganglion cells. Walter (1856, 1862) saw the 

 nerve ring and associated ganglia of Cosmocerca trispin- 

 osa ; he also saw the lateral, ventral and dorsorectal gang- 

 lia at the posterior end. But he confused the nervous 

 system with other structures. Schneider (1860) stated 

 that the nerve ring is the central organ and that struc- 

 tures described by other authors either were not pres- 

 ent or were misidentified. Bastian (1863) described two 

 "ganglionated chords" (now recognized as the lateral 

 chords) as the nervous system of Dracuncidus medinen- 

 sis. Schneider (1863) redescribed the nervous system of 

 Parascaris equortim as having a central organ or brain 

 in the form of a circumesophageal commissure, the nerve 

 ring, from which six anterior nerves extend to the ce- 

 phalic sensory organs and two subventral branches to 

 the venti'al chord. Ganglion cells were seen in the six 

 anterior nerves but it was noted that the lateral nerves 

 were not connected with the nerve ring. (This differenAr 

 is of fundamental importance and is further discusselT 

 on p. 162. He further stated that no special ventral 

 nerve exists and criticized Meissner, Wedl, and Walter 

 severely, stating that the transverse processes 

 from the muscles to the median chords were 

 muscles and that the cells seen were not 

 nerve cells. Bastian (1866) confirmed Schneider's ob- 

 servations and further noted that the nerve ring usually 

 has an inclined position with the dorsal side most an- 



teriad. He also noted that processes from the muscle 

 cells anterior to the nerve ring enter the nerve ring 

 directly while those posterior to the nerve ring join the 

 dirsal and ventral nerves. Bastian furthermore de- 

 scribed lateral and ventral ganglia posterior to the nerve 

 ring. Thereafter Schneider (1836) admitted the ex- 

 istence of median nerves. 



Butschli (1874) reinvestigated Ascaris lumbricoides and 

 Farascaris equorum recognizing the six anterior sensory 

 nerves with their ganglia and the lateral and ventral 

 ganglia connected with the nerve ring. He found that 

 some of the fibers of the lateral cephalic nerve passed the 

 nerve ring, entered the lateral ganglia and continued 

 through a liypodermal commissure (Cephalic lateroventral 

 commissure I) to the nerve ring by way of the sub- 

 ventral nerve trunks. Butschli also discovered first, the 

 laterodorsal somatic nerves whi'-h originate from the 

 dorsal part of the lateral ganglia; second, the latero- 

 ventral somatic nerves which originate from the sub- 

 ventral nerve trunks; and third, the ventrolateral somatic 

 nerves which originate in the lateral ganglia and in- 

 nervate the deirids or cervical papillae. In the posterior 

 part of the body he found that the fibers from the 

 nerve cells of the genital papillae are connected with 

 the ventral nerve via the hypodermis. He concluded by 

 stating that the question whether the transverse pro- 

 cesses from the muscles to the nerves are of muscle or 

 of nerve tissue remained unsettled but that its function 

 seemed clear. 



Rohde (1883-1885) discussed the nervous system of 

 the tail of Ascaris stating that the ventral nerve bi- 

 furcates anterior to the anus at which level there is a 

 hypodermal commissure (preanal lateroventral commis- 

 sure) to the lateral ganglia (lumbar ganglia) and a pair 

 of internal commissures passing around the rectum. 

 •Josenh (1882-1884). Rohde's former teacher, attempted 

 to claim this as his own work but the documentary 

 eviden:e is sufficient to convict him of plagiarism. He 

 obviously knew nothing about nematodes as is evidenced 

 by his single other paper (1879) on this matter in which 

 he identified a worm as AuaplecUis granulosus, giving 

 no de"cription but remarking on its unusual size for a 

 free-living nema (9 to 13 mm. long). This bears on 

 our case since he later referred to the ventral nerve as 

 being double in the same species. For various reasons, 

 we shall later show (p. 162) that this (double ventral 

 nerve) must have been the primitive condition just as 

 Meissner (1853) first indicated, but Joseph's publica- 

 tions should be ignored. 



Hesse (1892) working on Parascaris equorum estab- 

 lished the remaining general features of the nervous 

 system topography as we know them today. To Biitschli's 

 findings in the anterior part of the body Hesse added 

 several more hypodermal commissures including the latero- 

 ventral commissure II. In the mid-region of the body 

 of the female he discovered 30 dorsoventral hypodermal 

 commissures on the right side. 12 on the left, while in 

 the male he found 32 on the risht side and 13 or 14 on 

 the left. In the mid-region of the body of both sexes he 

 saw a pair of dorsolateral papillae (postdeirids Fig. 128) 

 connected with the lateral nerve and thence with the 

 ventral nerve. In the caudal region he obsei'ved that the 

 bifurcate ventral nerves unite with the lateral nerve 

 by way of the preanal lateroventral commissure. The 

 lateral caudal nerves formed by this union innervate 

 the so called "caudal papillae" of the female (phasmids). 

 In the male the preanal papillary nerve fibers join first 

 the lateral nerve where a ganglion cell is located thence 

 they return through the hypodermis to the ventral nerve 

 by the genito-papillary commissures. All later contribu- 

 tions concerning the nematode nervous system are to be 

 characterized as refinement work since no new major 

 points in the topographic anatomy of the nervous system 

 were added. 



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