glandular a:-tivity on the part of the periphery of the 

 vitellus, granules similar to the secretory g-ranules of 

 gland cells being present and the protoplasm being- 

 extremely vacuolate. Even in the egg production of 

 the trematodes in which specialized glands have (been 

 described presumably functioning in shell production 

 there is evidence (Kouri and Nauss, 1938) that the 

 shell is derived from the granules of the vitellus. Another 

 point of evidence of endogenous development of the 

 chitinous shell in the nematodes is the fact that after 

 assuming- a spherical shape the egg does not increase 

 in diameter as it would with exogenous development. 

 Figure 136 A shows the penetration of the vitellus by the 

 wedge-shaped sperm, the condensed gi-anular periphery 

 and the vacuoles. The vitellus varies slightly from 

 the typical pyramidal shape usually seen at this time. 



The chitinous shell is almost completed by the time 

 the egg reaches the uterus. The vitelline membrane has 

 formed within the shell but does not show the degree of 

 reticulation seen later. The protein coat is absent but 

 begins to form as the egg enters the uterus. At first 

 it is weakly mammillated and very thin. By the time 

 of the discharge of the first polar body it is a well- 

 established membrane. Figure 136B shows a uterine egg 

 at the time of the completion of the protein coat. The 

 vitelline meni'orane is diagrammatically represented in 

 our figure, but can be seen at this time. The vitellus 

 shrinks leaving a fluid cavity between it and the vitelline 

 membrane, the "Saftraum" of Wottge (1938), or the 

 peri-\atellus space. The tetrads of the first polar body 

 can he seen, and the condensed chromatin of the male 

 nucleus surrounded by the archoplasni. Figures 136C 

 and D show two types of mitotic figures in the production 

 of the first polar body. After division of the polar body 

 the dyads are left as in figure 136E. A second polar 

 body forms in the same manner. Figure 136F shows 

 the completely developed egg with the male and female 

 pronuclei. The two polar bodies can be seen, one against 

 the vitelline memlbrane and the other in the vitellus 

 which at this time is surrounded by a wide peri-vitellus 

 zone. The vacuoles have disappeared. 



Segmentation follows the release of the eggs from 

 the host. The first segmentation stage results from the 

 mitotic figure formed by the coalescence of male and 

 female pronuclear material. Cleavage and embryology 

 occur as showoi for Ascaris lumbricokJes, figures 137A 

 to H. 



The formation of the pattern of the protein coat of 

 parasite eggs is difficult to hypothesize. Some workers 

 describe molding chambers formed by constriction of the 

 genital tube. They assume that the eggs pass along the 

 duct single file and consequently the surface comes into 

 contact with the epithelial walls. This may be true in 

 some cases, but many of the most highly sculptored eggs 

 occur in all levels of the uterus of some species in such 

 numbers that their contact is problematical. This is 

 certainly true in Ascaridoidea. 



A more tena"ale theory of the development of the 

 external sculptoring might be advanced on the basic 

 precepts of colloidal behavior. The protein droplets in 

 the uterus have a fairly high degree of consistency. As 

 they come into contact with the shell they adhere at the 

 point of contact. They congeal, possibly through loss of 

 water absorbed by the vitellus, or possibly as a result 

 of increase of hydrogen ion concentration in the neighbor- 

 hood of the cell. Ascarid eggs have been shown by 

 Nolf (1932) to require oxygen which results in the 



Fis. 135. 



Xemic Ova. A-B — Anaplectus ffranulostts (A-ova, B-detail of shell, 

 showing layers). C — Rhabditis filiformis. D — Heterodera marioni. 

 E — RJmbditis stronpyloides. F — Heterodera marioni (Stage similar 

 to that named Oxynris iiicofjnita) , G — Tylenchinema oscinellae 

 (Stylet in adult worm within second cuticle), H — Mermis subnig- 

 rescens. I — Syphacea obvelata. J — Hetcroxynema cucullatum. K — 

 Oxyuronema atelophora. L — Travnema travnema. M — Enterobius 

 vermiriilaris. N — Oxyuris equi. O — Passalurus ambiyitus. P-Q — 

 Protrellus aureus (P — Cross section, Q — longitudinal section). R — 

 Pheiidonymus sp. S — Dermatoxys velicjera. T — Citellina marmotae. 

 U-V-W — Ascaris lumbricoides. X — Parascaris cquorum, Y — Toxas- 

 caris leonina. Z — Toxocara pteropodis. AA — Toxocara canis, BB — 

 Aplectana gigantica. CC — Heterakis gaUinae. DD — Oesophagostomum 

 radiatum. EE — Ascaridia lineuta. FF — Cyalhostoma amerlcanum. 

 GG — Aiuylostoma caniriitm. HH — Nematodirns fiUifOlis. II — 

 Necator americanus. JJ — Metastrongylus salmi. KK — Stephanurus 

 dpn'dlun. LL — Ascarid eggs (1-2 fertilized. .3-10 unfertilized). A-E, 

 P. Q. U and V. M. B. Chitwood. O. after Goodey. 1930. H. after 

 Cobb. 1926. K. after Kreis 1932. L, after Pereira. 1938. Z. after 

 Baylis, 1936. LL. after Otto. 1932. Remainder original, Christenson. 



Abbreviations -.ml, protein layer ; sh, shell proper ; vit m, vitelline 

 membrane. 



liberation of carroon dioxide as a waste. This might 

 produce a pH differential between the uterine fluid and 

 the periphery of the ^gg. If it is assumed that there 

 is a specific diff'erence in surface tension of the protein 

 droplets, and the assumption seems reasonable, there 

 would be a difference in size to the initial congealed par- 

 ticles. Subsequent addition of protein material would 

 maintain the difference resulting in sculptoring of differ- 

 ent degrees of prominence and different designs in the 

 various species. 



The production of specializations such as filaments 

 and byssi are even more difficult to visualize. If a fila- 

 ment were present as a central cord they could be 

 explained on the basis of adsoi'ption phenomena but no 

 such filament has as yet been demonstrated. 



Unfertilized eggs possess nc centrosome, have a gran- 

 ular appearing shell (Nelson) and a vitelline membrane. 

 In some eggs the shell is reduced to a barely discernible 

 membrane. The protoplasm is vacuolate from the time 

 of the formation of the vitelline membrane until it de- 

 generates. The protein coat may or may not be present 

 (Fig. 135LL). In some cases at least, both the vitelline 

 membrane and the true shell are apparently absent. In 

 the parthenogenic species, Rhabditis filiformis, no vitelline 

 membrane is formed in the developing eggs according to 

 Chitwood (unpublished observation). The same appears 

 to be the case in the parasitic generation of Strongyloides 

 ratti, while a vitelline membrane is present in developing 

 eggs of the foisexual free-living generation according to 

 Chitwood and Graham (1940). 



THE CHEMISTRY OF THE EGG MEMBRANES 



LEON JACOBS, WASHINGTON, D. C. 



There has been much confusion concerning the number 

 and kinds of membranes surrounding the developing 

 nematode embryo in the egg. Zawadowsky and his 

 collaborators (1914, 1928, 1929a, 1929b, 1929c) have 

 written a number of papers describing the egg membranes 

 of various species of Ascarididae, Trichostrongylidae, 

 and of Enterobius vermicularis (Oxyuridae) and Nema- 

 todirus spothiger {Trichostrongylidae) . In dealing with 

 eggs of Ascaris and related species these authors speak 

 of five memibranes, an inner lipoidal layer, three middle 

 layers which are designated membrana lucidn, and an 

 outer albuminous membrane which coats the egg; in 

 dealing with the eggs of the other species they studied, 

 they describe four membranes and homologize them with 

 the membranes of ascarid eggs. Dinnik (1930), a worker 

 in Zawadowsky's laboratory, figures four membranes, 

 excluding the plugs, on the egg of Trichuris trichiura. On 

 the other hand, Wottge (1937) and Chitwood (1938) 

 could demonstrate chemically only three layers on the 

 egg of Ascaris lumbricoides, and Jacobs and Jones (1939) 

 found only three membranes on the egg of Enterobius 

 vermicularis (by means of similar chemical tests. Chit- 

 wood (1938) also described three membranes, excluding 

 the plugs, on the eggs of Dioctophyma renale. It is diffi- 

 cult to interpret the homologies drawn by Zawadowsky 

 and his co-workers relating the five membranes of the 

 ascarid eggs to the four membranes they describe on 

 the ova of the other species. Nevertheless, the fact 

 that they designated the three middle layers of the 

 Ascaris egg as membrana lucida and based their descrip- 

 tions on the results produced with akohol treatment and 

 on the optical effects observed during the penetration of 

 cedar oil into the egg, indicates the solution of the 

 problem. The ^nembrana lucida undoubtedly corresponds 

 to the refractive part of the shell, which has been called 

 the homogeneous membrane by Wottge, and the shell 

 proper by Chitwood, and Jacolss and Jones. The latter 

 have pointed out that the chitinous shell of Enterobius 

 eggs is composed of two layers and that this layering is 

 probably the reason Zawadowsky and his collaborators 

 saw four different interfaces during the penetration of 

 cedar oil into the pinworm egg. Biedermann (1912) has 

 noted that the ichitin found on various animal forms 

 may be layered, and Schmidt (1936) has described differ- 

 ent" effects produced on plane polarized light by two 

 layers of the chitin of Parascaris equorum eggs. The 

 difference in the number of memlbranes described by 

 various authors can therefore be attributed to the variety 

 of techniques used in studying the eggs. Chemical tests 

 show the presence of three chemically different mem- 

 branes; physical tests detect the lamellation of these 

 membranes. 



177 



