protein coat as seen in eggs of Ascaris lumbricoides (Fig. 

 135U-W) and Dioctophyma renale (Fig. 141BB-CC). 

 Since there is a gradation between this type of external 

 modification into pitting, ridging, and simple rugosity it 

 seems proper to include all of these under a single 

 general term. Mammillation, to sonae extent, occurs in 

 most of the superfamilies of parasitic nematodes. 



The foregoing specializations of the eggs will be 

 considered in detail under the superfamily in which they 

 are found. 



Eggs of Free-living Nemas. M. B. Chitwood. Very 

 little information is available regarding the eggs of 

 free-living and plant parasitic nemas since they are 

 seldom used as taxonomic characters. In the Rhabditoidea 

 the eggs are usually of about the shape of the egg of 

 Rhabditis strongyloides (Fig. 135E), both shell and 

 vitelline membrane being simple and no protein layer 

 being present. In a few species, however (Diploscapter 

 coronata, Rhabditis filiformis and some ceplialobids) the 

 shell bears small protuberances (Fig. 135C) apparently 

 formed by an exceedingly fine protein layer. In some 

 parthenogenic species (Strongyloides ratti and Rhabditis 

 filiformis) Chitwood and Graham (1940), found no 

 vitelline membrane. In the Tylenchoidea, particularly 

 the family Tylenchidae, there is quite a bit of variation 

 in the relative length of the eggs, some species having 

 short, thick eggs {Aphelenchoides parietinus), others 

 rather narrow elongate eggs (Heterodera viarioni. Fig. 

 115 M & Q, and Aphelenchoides fragariae Fig. 119E). 

 Heterodera marioni is the only one of these producing a 

 protein substance and this is produced in a mass rather 

 than as an individual egg covering. 



Eggs with protuberances or spines are also known to 

 occur in a few species of free-living aphasmidians. These 

 include Anaplectus granulosus (Fig. 120C), Mononchus 

 punctutus according to Cobb (1917), and Trilobus pellu- 

 cidus according to Steiner (1916). Some chromadorids 

 have shells giving a punctate appearance. These species 

 with modified egg shells are the only members of the 

 Aphasmidia known to produce a protein layer. The 

 eggs of few other nemas have been observed outside 

 the parent so that, except for shape and relative size, 

 little is known. In some forms such as Chromadora sp. 

 (Fig. 120E) and Microlairnus fhiviatilis the eggs are 

 nearly spheroid while in others they are long and narrow 

 as in Achromadora minima, described by Cobb, (1918), 

 in which the mature egg is about one sixth the body 

 length. All sizes and shapes between these extremes are 

 known. 



Strongylina. (R. 0. C). Eggs usually with a thin, 

 smooth shell, composed of two layers, the chitinous shell 

 externally and the delicate vitelline membrane internally. 

 In some forms a mammillated protein coat is present, for 

 example Metastrorugylus salmi (Fig. 135JJ). Usually 

 there is a wide fluid cavity between the vitelline membrane 

 and the cell mass. The shape is that of a regular ellipse 

 in most species, but truncation has been reported for 

 some eggs. While most of the ova measure below 100 

 microns, in the family Trichostrongylidae measurements 

 approximating 300 microns have been reported. Oper- 

 culation is a rare condition but has been reported. In 

 most forms the ova are in early segmentation stages 

 when discharged; embryonated eggs are rare. A few 

 viviparous forms have been reported. A typical egg is 

 that of Necator americanus (Fig. 135II). 



Certain modifications of the egg envelopes occur in 

 this group which deserve mention. Eggs of Cyathostoma 

 possess an operculum at one pole as shown for C. ameri- 

 canum (Fig. 135FP). The chitinous shell of this species 

 is relatively thick and truncated at one pole. Beyond 

 it is a delicate extension enclosing a lenticular space. No 

 line of fracture is evident microscopically but it is at 

 this point the embryo leaves the egg envelope. The eggs 

 are unembryonated in iitero. Operculation has similarly 

 been reported in other representatives of the family 

 Syngamidae. 



As in the case of Cyathostoma americanum the shape 

 of strongyloid eggs often varies from the regular ellipse 

 characteristic of most species. In Nematodirus aspinnsus 

 the egg is atteni'atcd at one pole and truncate at the 

 other; similar truncation exists in one pole of the egg of 



Stephanurus dcntatus (Fig. 135KK). Eggs of Nemato- 

 dirus roscidus possess a rugose or alveolate shell. A 

 slight degree of striation appears in the shell of Nema- 

 todirus fillicolis. Some eggs are distinctly mammillated 

 {Metastrongylus salmi, et al). 



Eggs of the strongyloid worms are fairly uniformly 

 below 100 microns in length. In three genera of the 

 family Trichostrongylidae mammoth forms occur ranging 

 upwards of 300 microns. The largest egg of which we 

 have record is that of Nematodirus orientianus which 

 ranges from 25.5 to 272 microns in length. The genera 

 Marshallagia, Nematodirus, and Nematodirelia all con- 

 tain species with large eggs. 



There is some variation in the degree of uterine de- 

 velopment of the embryos in the superfamily Strongy- 

 loidea. The usual condition is that seen in eggs of 

 Necator americanus (Fig. 135II), Nematodirus fillicolis 

 (Pig. 135HH), or Stephanurus dentattis (Fig. 135KK), in 

 which early segmentation stages are seen. In eggs of 

 such forms as Dictyocaulus filaria and Metastrongylus 

 salmi (Fig. 135JJ) intra-uterine development of the 

 embryo occurs. Viviparity has been reported for the 

 genus Crenosoma and a few other genera. 



Figures 135DD and 135FF show the eggs of Oesoph- 

 agostomum radiatum and Cyathostoma americanum re- 

 spectively after incubation outside the host. 



OxYUROlDEA. (R. O. C). The eggs of the superfamily 

 Oxyuroidea are usually described as possessing a double- 

 contoured shell flattened on one side. The double- 

 contoured appearance is due to the presence of the 

 protein coat and the chitinous shell forming the external 

 investment. Internally is the vitelline membrane of 

 considerable thickness and duraibility in some species. 

 In general the eggs are small but some species run 

 above 100 microns in length, for example Syphacea 

 obvelata. (Fig. 135 I). The eggs of some species possess 

 polar filaments, equatorial filaments, opercula and mam- 

 millation of the shell. 



Polar filaments are found in the eggs of Citellincb 

 marmotae and other species of the genus. Mantor (1930) 

 describes the eggs of this species as thin-shelled, elongate 

 oval in outline, and somewhat flattened on one side. From 

 each pole there arises a long filament, broader at its 

 base where it is attached to tlie outer shell and tapering 

 to a fine thread. The filaments are equal in length and 

 normally possessed by all eggs (Fig. 135T). 



Peculiar equatorial filaments occur on the eggs of 

 Pscudoyiymus sp., a parasite of certain aquatic beetles. 

 The normal number is two, but they may occur singly. 

 They originate from a cone-like papilla on the protein 

 coat and coil spring-like about the egg in utero. At 

 oviposition the filaments unwind, rotating the egg on its 

 long axis. The eggs are embryonated at the time of 

 discharge (Fig. 135R). 



Operculation is quite commonly seen in the Oxyuridae. 

 Bipolar operculation is possessed by eggs of Pharyngodon 

 spinicauda. The asymmetrical eggs of this species have 

 prominent polar caps. In Oxyuris equi (Fig. 135N) a 

 single operculum is present, the egg being somewhat 

 similar to those of typical trematodes. The chitinous 

 shell in this species is incomplete at one end, as is seen 

 in the opercular apertures of the Trichuroidea, the end 

 being closed by a thin, protein deposition. The egg 

 of Dermatoxys veligcra has a subpolar operculum marked 

 by a prominent line of fracture (Fig. 135S). In the 

 case of eggs of Citellina marmotae the operculum is like- 

 wise subterminal. The protein coat is evenly striated 

 over its entire surface except at a point near one pole. 

 Here the striation is lost -and the membranes become 

 thin. This marks the opercular spot described by Mantor 

 (1930), appearing as shown in figure 135T. 



Mature eggs of Dermatoxys veligcra have excrescences 

 over the surface giving the shell a striated appearance 

 (Fig- 135 S). Freitas and Almeida (1936) describe two 

 longitudinal ridges, which are strongly striated trans- 

 versely, for tho eggs of Hetcrox'ynema wernicki. Chit- 

 wood "(1932) describes a lateral crest on the flattened eggs 

 of Protrellus aureus (Fig. 135P-Q). 



Some workers lay much stress on the shape of the 

 egg as a diagnostic character. The case which comes 

 to mind is Kofoid and White'.s "O.ryuris incognita" which 

 was described on the basis of asymmetrical eggs passed 



182 



