Trichuroidea. (R. O. C.)- The eggs of the Trichuroidea 

 possess three membranes; an outer protein coat which 

 may be deeply pigmented presenting a brownish color; 

 an intermediate true shell which is usually transparent, 

 and an internal vitelline membrane which may be 

 granular or possess reticulations (Fig. 141V). The most 

 characteristic structures are the plug-like opercula at 

 either pole. These penetrate the protein coat and the 

 true shell, but not the vitelline membrane. In some 

 species the opercula are very prominent, projecting well 

 beyond the protein coat externally, and well into the 

 egg cavity internally {Tricluiris oris, Fig. 141Y). In 

 others they conform in length with the polar thickness 

 of the egg envelope presenting even contours both ex- 

 ternally and internally (Ttichuris vtdpis. Fig. 141X). 

 The cuticular shell projects along the sides of the oper- 

 cula forming collar-shaped sockets into which the oper- 

 cula fit. The internal limits of the opercula widen beyond 

 the diameter of the opercular apertures making them 

 difficult to dislodge by mechanical means. Under pressure 

 the egg-capsule itself will often break before the oper- 

 cula are dislodged. The eggs are usually unsegmented 

 at the time of discharge. 



The appearance of the protein coat varies considerably. 

 Thomas (1924) describes the eggs of Trichosomoides 

 crassicauda as rugose. When the eggs of this species 

 are discharged they are held together in stringy masses 

 by a sticky secretion. This condition has also been re- 

 ported by Walton (1923) for Capillaria lorigistriata and 

 it occurs in the spiruroid genus Gonglonenia. Pologentsev 

 (1935) notes a striated appearance in the protein coat 

 of ova of Trichuris busulka. A similar striation exists 

 in Capillaria aerophila as shown by our studies (Christen- 

 son, 1935). 



The eggs of Capillaria magalhaesi are described by 

 Lent and Freitas (1937) as marked by circular and oblique 

 striae. Baylis (1934) notes a punctate appearance of 

 the shell of Capillaria lophortygis, and in Capillaria 

 brevicollis and Capillaria inequalis it is mammillated 

 (Walton, 1935). Faust and Martinez (1935) describe a 

 striated or channeled sculptoring externally for the 

 eggs of Cajnllaria hepatica. 



Size has little diagnostic value in the ova of this group. 

 Species of Trichuris give measurements which overlap 

 and are therefore not significant (Chandler, 1930). The 

 same is true for the genus Capillaria. It is of some value 

 in separating species of Trichuroidea which may be 

 present in a single host (Christenson, 1935). 



Although usually considered viviparous our studies 

 show that Trichinella spiralis is actually ovoviviparous. 

 Immature females removed from the intestine of rats 

 possess typical, thin-shelled eggs of the type shown in 

 Figure 141 AA. The thin chitinous shell presents a slightly 

 yellowish tinge and in spots the vitelline membrane was 

 observed to have pulled away from it. Hatching occurs 

 in utero, the minute larvae being discharged with no 

 noticeable embryonic investments. 



Figures 141V to AA show the eggs of some of the 

 common trichuroid species occurring in man and domest- 

 icated animals. 



Mermithoidea. (R. O. C). The bizarre eggs of the 

 mermithoid worms have received much attention from 

 biologists since they were first noted. Dujardin (1842) 

 describes the eggs of Merniis nigrescens observing the 

 peculiar, branched filaments termed byssi. (Fig. 139-140). 

 Meissner (1856) further described the eggs of a form 

 he considered to be the same species, noting their lenticu- 

 lar shape, the brownish color, and the two membranes 

 composing the egg envelope enclosing a developed larva. 

 He obsci-ved the transverse line of junctui-e of the outer 

 ihell, the polar thickenings, and the byssi arising from 

 them as cords ending in tassel-like branches a short dis- 

 tance from the egg. He described the outer shell as 

 essentially colorless, the brown color of the egg envelope 

 being due to the pigmentation of the cuticular shell, or 

 chorion. 



Cobb (1926) expressed the view that the species 

 studied by Meissner was not Mennis nigrescens of 

 Dujardin but a different species which should be termed 

 Mermis nieissneri. He described a new species of Mermis 

 under the nam? M. subnigrescens and presented an ex- 

 cellent figure of the egg (Fig. 135 H). He described 

 the byssi as flexible, branched, entangling filaments which 

 arise from polar elevations. He, also, noted the equatorial 

 line of juncture between the two halves of the outer 



shell. Within the shell he shows the outline of the 

 coiled larva with its three-pronged spear. 



Christie (1937), like Meissner, observed the concen- 

 tration of the pigment in the inner shell. This envelope 

 is described as being spherical in outline and slightly 

 compressed at the poles. No mention is made of ^he 

 presence of a vitelline membrane but such a structure 

 is shown in one of his figures (Fig. 139-140). 



From the foregoing review it is apparent that the 

 outer "shell" described by difl"erent authors is compara'ble 

 to the protein coat, and that the byssi associated with 

 it are not alien in origin to the terminal filaments of 

 other forms. This view is supported by Meissner's 

 description of the intra-uterine formation of the outer 

 shell. The inner shell, or chorion, is the same as the 

 chitinous shell of other groups, and that a vitelline 

 membrane is present is indicated by Christie. Christie 

 shows that hatching is ac:ompanied by the fracture of 

 the eggs at the polar thickenings (Fig. 140) similar 

 to the condition reported by Ransom (1904) in the 

 hatching of Oxyspirura mansoni, leaving the barrel-shaped 

 shell remnants. 



Some workers have been impressed with the similarity 

 between the eggs of the Mermithoidea and those of the 

 Trichuroidea. They point out that the thickened portion 

 of the outer shell containing the byssi might be compared 

 to the opercula in the latter group, and that in other 

 details the eggs are similar. The analogy is even more 

 apparent in non^byssate forms. Steiner (1938) states 

 that the eggs of Pseudomerniis vanderlindei are oval in 

 shape, with heavy shells having both ends truncate, and 

 containing fully developed embryos. He points out that 

 they distantly resemble the eggs of the Trichuridae. 



The lenticular shape assigned to eggs of some of the 

 Mermithoidea is well seen in those of Tetradonenw plicans 

 as pointed out by Hungerford (1919). The eggs of this 

 form are thick-shelled, somewhat testaceous in color, 

 and disc-shaped in outline. When on edge an oblong 

 contour is presented. These peculiar eggs are retained 

 under the cuticula of the female after oviposition. All 

 stages of embryonic development are seen in utero. 



In some nematodes it has been observed that the first 

 embryonic molt occurs within the egg envelope. This 

 has been noted to be the case in the egg of Aganiermis 

 decaudata by Cobb, Steiner and Christie (1923). 



DlOCTOPHYMATOIDEA. (F. G. WALLACE). The OVa of 



the superfamily Dioctophymatoidea are unique among 

 nematode ova in the form of the outer coat of the egg 

 shell which is deeply pitted with funnel-shaped de- 

 pressions. As representative of the group we may take 

 the egg of Dioctophyma renale, which is symmetrically 

 oval, 64 to 80 microns in length, and 36 to 48 microns 

 in width (author's measurements). The shells of speci- 

 mens dissected from the uterus of preserved forms are 

 colorless, while those taken from urine-contaminated 

 feces are brown. The surface of the shell is pitted with 

 irregular-shaped depressions 4 to 7 microns each in great- 

 est diameter. (Fig. 141BB-iCC). The wall of each pit, when 

 seen either in surface view or in optical section, appears 

 to have a double contour. The surface of the shell be- 

 tween the pits is smooth. At either end of the egg, the 

 shell bulges slightly, is free from pits, and is colorless. 

 These clear ends are spoken of as terminal plugs. 



The shell appears to consist of three layers; the 

 external pitted coat or cortical layer, the inner shell, and 

 the vitelline membrane. The terminal plugs though 

 somewhat different in chemical composition, belong struc- 

 turally to the outer coat. The entire shell measures 6.8 

 to 8 microns in thickness along the equator of the egg and 

 reaches 12 microns in the terminal plugs. The greater part 

 of this thickness (4.5 microns at the equator and 8 to 9 

 microns at the terminal plugs) is occupied by the cortical 

 layer. 



The studies of Chitwood (1938) and Lukasiak (1930) 

 on the chemical composition of the various layers are 

 in part inconclusive as formalin-preserved material was 

 used, but it appears that the inner shell is probably 

 chitinous. The terminal plugs differ from the rest of 

 the cortical layer in being more soluble in KOH, 

 sulphuric acid, sodium hypochlorite, and nitric acid. 

 According to Balbiani (1870), whose figures of 

 the egg have been copied directly or indirectly 

 by most subsequent authors, the terminal plugs are the 

 weakest points in the shell, as when embryonated eggs 

 were subjected to cover-glass pressure the embryos es- 

 caped at the ends. 



186 



