Topographic Anatomy 



The most thoroughly studied species are, of course, 

 Ascaris hitnhricoides and Parascaris equoruvi due to the 

 investigations of numerous early workers including Hesse 

 (1892) and concluding with Goldschmidt (1908). We 

 shall describe the anatomy as found by those workers 

 in Ascaris in order to have a point of departure. The 

 nervous system is divisible into four parts; the central, 

 the peripheral, the recto-sympathetic and esophago-sym- 

 pathetic systems. The latter has already been described 

 (p. 95) ; it is connected with the central nervdus systems 

 by a pair of ventrolateral nerve fibers extending anteriad 

 from the nerve ring. 



1 



Fig. 128 



Diagrams ot nervous system of Ascaris. A — Female dissection. 

 Ventral view. B — Male dissected, ventral view. C — Male tail, 

 reconstruction (preanal papillae omitted). A-B after Brandes 

 1899, Abhandl. Naturf. Gesellsch. Hallo, v. 21. C — Based on 

 Voltzenlogel, 1902, Zool. Jahrb. Abt. Anat., v. 16 (3) : 481-510. 



Topographic Anatomy of Ascaris lumbrlcoides 



Central nervous system. We classify as central ner- 

 vous system the ganglia connected with the nerve ring, 

 the nerve ring, and the ventral ganglion chain which is 

 termed the ventral nerve. Attached to the anterior side 

 of the nerve ring there are six small cephalic papillary 

 ganglia — two subdorsal, two lateral and two subventral 

 (Fig. 129 D). Fibers from the posterior side of these 

 ganglia pass directly into the nerve ring while fibers 

 from the anterior side form the six cephalic papillary 

 nerves. These nerves may be compared with the cranial 

 nerves of vertebrates since their cells are situated in the 

 chief part of the central nervous system. Anterior to 

 the nerve ring there is also a commissure connecting the 

 dorsal and ventral sides of the nerve ring; this asymmet- 

 ric commissure consists of a nerve fiber extending an- 

 teriad from the dorsal side of the nerve ring in the 

 dorsal chord half way to the anterior end, then turning 

 right, through the hypodermis to the ventral chord, 

 thence posteriad to the anterior face of the nerve ring; 

 this is called dorsoventral covimissure I. Attached 

 to the posterior side of the nerve ring there is a small 

 dorsal ganglion in which the dorsal somatic nerve origi- 

 nates; there are also two small subdorsal ganglia and 

 two large ventral ganglia. In the lateral area in the 

 region of the nerve ring there are two large masses of 

 nerve cells which are generally referred to as the lateral 

 ganglia. Their neurones are of many different types and 

 their fibers connect with the nerve ring in various ways. 

 Sometimes, as in Ascaris, the lateral ganglia may (be 

 subdivided. Goldschmidt termed the groups of lateral 

 cells which lie directly against the nerve ring and con- 

 nect with it, the internal lateral ganglia. There is a pair 

 of large hypodermal commissures, the major lateroventral 

 commissures connecting the major part of the lateral 

 ganglia with the nerve ring by way of the massive 

 paired subventral nerve trunks. Several subdivisions of 

 the lateral ganglia have processes into these commissures. 

 The largest are the amphidial ganglia which connect an- 

 teriad with the amphidial nerve, the others being the 

 posterior internolateral ganglia and the anterior extemo- 

 lateral ganglia. The other two subdivisions of the lateral 

 ganglia, the median and posterior extemolateral ganglia 

 are connected with the ventral nerve through a second 

 pair of hypodermal commissures, the ininor lateroventral 

 commissures. One of these, the median extemolateral, is 

 also connected anteriad with the nerve ring. After giving 

 off the major lateroventral commissures the subventral 

 nerve trunks unite forming the ventral nerve which is 

 in reality a chain of ganglia. The first and largest of 

 these is called the retrovesicular ganglion; it is situated 

 just posterior to the excretory pore at some distance 

 posterior to the minor lateroventral commissures. 

 Throughout the body asymmetrically placed dorsoventral 

 commissures connect the dorsal and ventral nerves. A pair 

 of symmetric dorsoventral commissures, the anterior 

 dorsoventral commissures, originates from the anterior 

 side of the nei-ve ring at a point posterior to where it 

 joins with the major lateroventral commissure. There 

 is also an asymmetric dorsoventral commissure passing 

 by the posterior extemolateral ganglion and proceeding 

 anteriad to join the ventral nerve near the ventral ganglia; 

 this is called the oblique dorsoventral commissure. Since 

 all of these structures are rather closely associated with 

 the nerve ring, they may be classified as central nervous 

 system. Further groups of cells of nervous character 

 are found throughout the length of the ventral nerve, 

 groups being distinct in some species though not in 

 Ascaris. The ventral nerve passes to the right of the 

 excretory pore and vulva. Posteriad it gives off two 

 internal branches, the rectal commissures, which extend 

 through the ibody cavity and unite dorsal to the rectum; 

 in the course of each of these commissures there is a 

 latero-rectal ganglion. There is a dorso-rectal ganglion 

 where the two commissures unite and from it the median 

 caudal nerve extends posteriad first in tlie dorsal pulvillus, 

 then in the ventral chord. Since both the commissures 

 and ganglia are merely a branch of the ventral nerve 

 the whole complex might be considered as a rectal sym- 

 pathetic system. Posteriorly the ventral nerve ends by 

 more or less bifid preanal ganglia from which the paired 

 hypodermal ano-lumhar commissures extend to the lateral 

 chords where they join the lateral nerves near the 

 lumbar ganglia. 



160 



