CHAPTER IX. 

 THE EXCRETORY SYSTEM 



M. B. CHITWOOD and B. G. CHITWOOD 



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Introduction 



The structui-es which at present are termed 

 "excretory" system have been the subject of many 

 arguments into which little evidence has been 

 introduced. An excretory function has not aluays teen 

 presumed for these structures and in some nistan.es 

 other structures have been termed excretory organs. 



Bojanus (1817), studying Parascaris equoriim, discov- 

 ered a pair of lateral vessels contained within the lateral 

 chords and anastomosing in a bridge beyond which they 

 continued. Later (1821) the same author thought he 

 saw a row of lateral stigmata in Kliaphidascaris acus and 

 he (finally concluded that the lateral canals were blood 

 vessels and the "biischelformigen Organe" with which 

 they are sometimes associated were gills. 



Cloquet (1824) likewise observed lateral vessels and 

 their anastomosis anteriorly; it was his opinion also 

 that the vessels were circulatory. Mehlis (1831) observed 

 a gland opening near the head in Contracaecinn spicu- 

 ligernm and paired strand-like bodies (glands) in strongy- 

 lids opening at the mouth. He presumed both to be 

 salivary glands, but Schneider later interpreted these 

 structures as excretory glands in both cases. 



Shortly thereafter von Siebold in an appendix to a 

 thesis by Bagge (1841) noted the existence of a ventral 

 pore connected with paired lateral canals in Osivaldocru- 

 zia (Strongyles auricidaris) and Aplt-ctana. (Ascaris 

 acuminata) but he did not, at that time, express any 

 view to the function of these structures. 



Blanchard (1S47) injected specimens of Ascaris lumbri- 

 coides and upon seeing a large ovoid body in the left 

 lateral chord (the gland nucleus. Fig. 112H) he decidtd 

 that he had found the heart and he also maintained that 

 there is a second pair of vessels just under the cuticle. 

 On this basis he decided this system to be circulatory. 



Leidy (1853) observed a "follicle communicating with 

 the exterior and having its bottom connected by means 

 of radiating bands to the external surface of the alimen- 

 tary canal" in Thelusioma attenuatum and Aorurus agile. 

 He was followed by Huxley (1856) and Wagener (1857) 

 who recognized the full extent of the lateral vessels in 

 Oswaldocruzia filiformis (Strongylus auricularis) and 

 Heterakis sp., respectively. It was at this time that 

 Davaine (1857) described a ventral tube and a lateral 

 vessel (on one side only) in Anguina tritici. 



Schneider (1858, 1860, 1863, 1866) was the first worker 

 to draw the various isolated bits of information together, 

 synthesize, examine critically and summarize. He first 

 proved Blanchard's concept regarding Ascaris lumbricoides 

 to be erroneous, showing that what was interpreted as 

 the heart is a large nucleus in the vessel wall, that 

 there is only one pair of vessels and they unite to open 

 through the ventral pore. He likewise established the 

 fact that the ventral pore and canals are joined in the 

 oxyuroids and strongylins; he saw the labyrinthoid coils 

 of the posterior termination of the vessels in Alloionemu 

 uppendiculatum; and also observed the two strand-like 

 bodies ("Subventral" or "cervical" glands) that are at- 

 tached to the anastomosis or bridge in Rhabditis strongy- 

 loides and Strongylus spp. He further expressed the view 

 that lateral vessels are present in all "mero" and "poly- 

 myarian" nemas and usually absent in "holomyarian" 

 nemas (except Anguina tritici) ; and finally he (1866, p. 

 220) concluded that this system of vessels must be re- 

 lated to the excretion of chemical waste products as in 

 the excretory system of all other worms. 



Mieanwhile Eberth (1860, 1863) erroneously described 

 paired lateral vessels in Heterakis galliuae, with two 

 anterior and two posterior lateral openings (amphids and 

 phasmids respectively) and in Passaturus he apparent y 

 did not differentiate between vessel and chord- In refer- 

 ence to marine nematodes he was more accurate in 

 describing a fine pore near the head and a clear tube 

 proceeding posteriorly in the esophageal region of 

 Oncholaimus, Enchelidium, and Enoplus. 



Bastian (1866) verified many of Schneider's observa- 

 tions, proved the general existence of a "ventral" gland 

 in marine and fresh water nemas and definitely showed 

 that the "water vascular system" (vessels) in parasitic 

 nemas and the ventral gland in free-living forms "are 

 only modifications of one and the same structure." Whi.e 

 drawing attention to a similar system in trematodes he 

 noted that in no instance have vibratile cilia been ob- 

 served in the canals of nematodes and that in neither 

 nematodes nor trematodes is the system adapted to res- 

 piratory activity. He concluded that it must be excre- 

 tory. 



General Morphology. The diversity of the nemic 

 excretory system makes it a difficult system to interpret. 

 The general concept of a unicellular system probably 

 originated with Bastian's homologizing of the single 

 ventral gland of marine nemas with the tubular system. 

 Though neither Bastian nor Schneider emphasizes the 

 point, only one nucleus (the sinus nucleus) was known 

 in Ascaris; nevertheless they knew of two cells associated 

 with the sinus in rhabditids and strongylins (Fig. 112 

 I-L). Cobb's description (1890) of the origin of the 

 excretory system in the first stage larva of Enterobius 

 vermicularis as an outgrowth of a single invaginated 

 hypodermal cell has given much impetus to the primary 

 single cell concept. Later (1925) the same author de- 

 scribed the system in mature embryos of Rhabditis 

 ico^iensis as consisting of a single gland cell, terminal 

 duct, and paired lateral canals in a ventral position, i. e., 

 not in the lateral chords; according to his view the 

 paired subventral glands are derived from the single 

 cell by splitting and the canals are merely outgrowths. 

 Study of the excretory system in young specimens is 

 technically very difficult and open to considerable error 

 due to the delicacy of the structures. As indicated by 

 Cobb's own figures and verified in diverse instances by 

 the writers the system in first stage larvae is much 

 nearer to that of the adult than is commonly supposed. 

 Actually, we have been unable to establish with certainty 

 any difference between larva and adult. In our opinion 

 the common pors and cell illustration in larval nematodes 

 represents only the obvious features. The fact that 

 neither Cobb nor other adherants of the unicellular gland 

 idea have accounted for or even recognized the existen.e 

 of a terminal duct cell in addition to glands or sinus 

 cells makes us most dubious of the entire concept. 



The second concept of the system is based upon its 

 identity with the protonephridial system of trematodes, 

 rotifers, gastrotrichs, etc. This viewpoint was accepted 

 by Bastian (1866) and Schneider (1866) without particu- 

 lar question. It likewise seemed reasonable to Biitschli 

 (1876) and Martini (1916). It has fallen into disfavor 

 recently because it cannot be accepted by those presuming 

 the marine aphasmidian (having a single ventral gland 

 cell) as primitive. These authors (Filipjev, Stekhoven) 

 must assume the system to arise de novo in the Nematoda 

 or assume that the remainder of the Animal Kingdom 

 arose from nematodes. They have apparently chosen the 

 first alternative though with odd consistency at the same 

 time relating nematodes, rotifers, echinoderes, gastrotrichs 

 and nematomorphs. Steiner (1919, 1920) brought out a 

 series of diagrams hypothetically indicating the mode of 

 evolution of the nemic excretory system from that of the 

 rotifer. His diagrams give interesting points but over- 

 look the essential complexity of the tubular system of 

 coth groups. We shall not go into such matters at the 

 present. The most necessary evidence, critical embry- 

 ological study, is lacking. 



Golowin (1902) expressed the view that the tubular, 

 cuticularly lined terminal duct cell is an invagination 

 of the hypodermis which meets and fuses with the lateral 

 canals and excretory sinus. This view was concurred 

 in by Goldschmidt (1906) and has rather significant 

 support. It accounts for the collecting tubes as a sepa- 

 rate entity, not developed from a ventral gland; these 

 tubes may be considered as derivatives of the basic 

 protonephridial system without reorientation of the 

 system; it accounts for the minimum two to three cell 



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