CHAPTER X 

 THE REPRODUCTIVE SYSTEM 



B. G. CHITWOOD and M. B CHITWOOD 



Introduction 



The reproductive system is more or less similar in 

 both sexes of all nematodes, being composed of one or 

 two (rarely multiple) tubular gonads, each gonad being 

 comparable to a single testicular or ovarial tubule of 

 arthropods or vertebrates. 



Sexual dimorphism is, as a rule, limited to characters 

 of the reproductive system such as the vulva and male 

 copulatory apparatus (bursa, spicules, genital papillae) 

 but it is manifested to a minor extent in the fact that 

 females are nearly always larger than males. Among 

 the parasitic species this tendency becomes most marked 

 in Trichosomoides crassicauda in which the male is so 

 small that it enters the female by way of the vulva and 

 spends its life within the uterus (Fig. 115 D). Other 

 marked but less spectacular cases are those of Dracun- 

 culus medinensis and Philometra globiceps in which the 

 female becomes 18 and 33 times as large, respectively, 

 as the male. In these cases, however, the female con- 

 tinues growth after copulation takes place. Howardida 

 benigna ( Allantonematidae) presents a similar case of 

 copulation in a juvenile stage but afterwards the young 

 female enters a new host where it undergoes the greater 

 part of its development. 



Sexual modifications of gross body form are rare and 

 usually take a single course, the enlargement of the 

 female so that she becomes a reproductive sac — Heterodera 

 (Fig. 115 N), Tftrameres (Fig. 115 C), and Tylenchidus. 

 The lobes of Phlyctainophora may only be the result of 

 growth in a confined situation. The Allantonematidae 

 (inhabiting the body cavity of insects) present more 

 examples of reproductive sac formation than do all other 

 nemic groups combined. In this group we find Tylen- 

 chinema (Fig. 115 J), Chondronema, Scatonema (Fig. 

 115 E), and AUaHtonema (Fig. 115 I) all of which show 

 progressive stages of degeneration of the female to re- 

 productive sac formation. Tripius (Fig. 115 K) and 

 Sphaerularia (Fig. 115 A-B), of the same family, go 

 much further in degeneration; after copulation of the 

 precocious free-living adults the females enter the new 

 host and growth of the reproductive system takes place 

 at the expense of the remainder of the body. The uterus 

 with the ovary enclosed is everted and continues to 

 grow until it is many times as large as the female body. 



Most of the remaining types of sexual dimorphism are 

 attributed to failure of the male to attain complete 

 development, such are the sexual differences in cephalic 

 characters, esophagus, and cuticle of thelastomatids. 

 Seurat (1920) considered the alae and spines of the 

 male of Tstrameres fissispina as organs of propulsion 

 and fixation necessary to its free life in the succcnteric 

 ventricle of its host and migration to the female, which 

 lives sedentarily in the gastric glands of its host. Sexual 

 dimorphism in free-living nemas is extremely rare, the 

 most outstanding examples being members of the En- 

 chelidiinae; in some of these forms there may be com- 

 plete degeneration of stoma in the adult male (Enchel- 

 idiiim pauli Fig. 63 I-J). In male tylenchoids, the stylet 

 is often not as well developed as that of the female, 

 Hexatylus abulbosi^s (Syn. Neotylcnchus abulhotius) being 

 an extreme example of this type of dimorphism. Sexual 

 dimorphism in size of amphids, those of the male being 

 the larger, has been described in such forms as Trilobits 

 gracilis var. homophysalidis, Ironus ignavus and some 

 mermithids. 



Intersexes. Meissner (1853) first observed male sec- 

 ondary sexual characters (spicules and genital papillae) 

 in normal female Hexamermis albicans. Such forms 

 were erroneously regarded as hermaphrodites but this 

 is a false impression as only one set (female) of repro- 

 ductive organs is developed. Since the time of Meissner 

 such intersexes have been described in Enoplus communis 

 (syn E. cochleatiis) by Schneider (1866), in Chromadora 

 poecilisoma and Thoracostoma figuratum by de Man 

 (1893), in Porrocaecum heteroura by Willemoes- Suhm 

 (1869), in Tribolus diversi-papillafus by Daday (1905), 

 Trilobus gracilis hy Vitievsen (1911), W. Schneider (1922) 

 and Linstow (1903). Hagmeier (1912), Steiner (1923) 



and Christie (1929) have described intersexes iiT' 

 thids. The latter author found that sex is determined 

 by the number of parasites in a host. When one to 

 three parasites were present in grasshoppers they were 

 females, when four to 23, they were mixed, and when 

 above 23 they were all males. By feeding a known 

 number of parasite eggs to the host, Christie determined 

 that the sex ratios were not due to selective mortality. 

 The fact that intersexual males are unknown seems to 

 cast doubt upon the theory that the sexes are primarily 

 present in equal numbers and may be converted to the 

 opposite sex by the influence of environmental factors. 

 Nevertheless, intersexes seem to be related to crowding 

 and when a single female is present in a host containing 

 10 males, it is conceivable that they might cause her to 

 be an intersex. 



General Morphology 



So long ago as 1866 Bastian remarked on the difference 

 between the reproductive systems of free-living and 

 parasitic nemas; he felt that the relative simplicity of 

 the system in free-living nemas was sufficient ground 

 for the separation of that group from parasites as a 

 separate family (Anguillulidae, equivalent in scope to 

 our Rhabditina, Chromadorida, Enoplina and Dorylai- 

 moidea). The greater complexity of the reproductive 

 system in parasitic nemas is chiefly limited to the female 

 sex and is correlated with increased egg production. 



Division of the nemas into taxonomic groups on the 

 basis of the reproductive system has been proposed by 

 only one modern author, Rauther, (1918, 1930) who 

 divided the Class Nematoda into two orders: Telogonia 

 (includes Phasmidia, Chromadorida, Enoplina, Dorylai- 

 moidea and Mermithoidea) and Hologonia (Trichuroidea 

 and Dioctophymatoidea). These divisions apply to both 

 sexes. The germinal zone in the order Hologonia (exam- 

 ples Trichuris frichiura as observed by Eberth, 1869, 

 and Dioctophyma renale as obsei-ved by Leuckart, 1876, 

 (p. 378) extends the entire length of the gonad, being 

 composed of a series of germinal areas ()n one side of 

 the gonoduct in the former and comprising the entire 

 circumference of the gland in the latter. In neither case 

 is a rachis present and the entire group Hologonia is 

 characterized by the presence of a single gonad in tioth 

 sexes. In the majority of nemas (Telogonia) it is a 

 well established fact that new germ cells originate only 

 at the end of the gonad. However, only a small propor- 

 tion of the Nemata (particularly parasites) has been 

 well studied from this standpoint. Data regarding mermi- 

 thids and Cystoopsis should be particularly informative 

 but are lacking to date. 



Eschricht (1848) discovered that in the female ascar- 

 idids germ cells are not free in the gonoduct but are 

 grouped around a central axis which is termed the rachis. 

 Subsequent authors have found this structure to be a 

 common feature of ascaridids, oxyurids, strongylins, and 

 spirurids. Some, including Biatschli, compared the rachis 

 to the cell of Verson or apical cell of the gonads of 

 insects, but as pointed out by Seurat (1920) the rachis 

 is not a constant feature of nemas even in special 

 groups, (it is present in Bradynema, absent in Ditylen- 

 chns) and it does not supply yolk, for the nucleus and 

 protoplasm grow in the same proportion as the oogonium 

 passes down the tube. The function of the rachis is not 

 understood and its apparent erratic occurrence seems 

 to eliminate it as an ordinal character. 



The genital primordium is identical in that it consists 

 of two germ cells and two epithelial cells in the first 

 stage larva of both sexes of all nemas studied. In forms 

 with two gonads the primordial germ cells are thereafter 

 separated by somatic cells, one germ cell entering each 

 gonad, while in forms with one gonad the germ cells 

 remain together. In two-ovaried forms the intervening 

 cell group forms the two uteri and connects with the 

 vagina in the female, or forms the vas deferens in the 

 male. It would therefore, seem obvious that two gonads 



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