ToRNQUlST, N. 1931. — ^Die Nematodenfamilien Cucullan- 

 idae und Caniallanidae etc., Goteborgs K. Veteiisk. 

 — o. Vitterhets— Samh. Handl., 5., f., s. B, v. 2 (3), 

 441 pp., pis. 1-17. 



VOLTZBNLOGEL, E-. 1802. — Untersuchungen iiber den ana- 

 tomischen und histologischen Bau des Hinterendes 

 von Ascai'is megalocepliala und Ascaris liimbricoides. 

 Diss. 32 pp., 3 pis., 20 ivgs. Jena. Also in Zool. Jahrb., 

 Abt. Anat. v. 16 (3): 481-510, pis. 34-36. 



Walter, G. 1856. — Beitrage zur Anatomie und Physiologie 

 von Oxijuris ornafa. Ztschr. Wiss. Zool., v. 6 (2) : 

 163-201, pis. 5-6, figs. 1-28. 



1898. — Fernere Beitrage zur Anatomie und 

 Physiologie von O.ryiiris ornata. Ibid., v. 9 (4) : 485- 

 495, pi. 19, figs. 29-'34. 



1862. — 'Beitrage zur niikroskopischen Anatomic 

 der Nematoden. Arch. Path. Anat. Berlin, 24 J, 2 F., 

 V. 4 (1-2): 166-182, pi. 3, figs. 1-19. 



1863. — Mikroskopis:-hc iStudien uber das Central- 



Nervensystem wirbelloser Thiere. 56 pp., 4 pis., Bonn. 



Wedl, C. 1855. — Ueber das Nervensystem der Nematoden. 



Sitzungsb. Konigl. Akad. Wiss. Wien, Math.-Naturw. 



CI., v. 16 (2) : 298-312, 1 pi. figs. 1-10. 



CHAPTER XII 

 NEMIC OVA 



REED O. CHRISTENSON, Dept. Zoology-Entomology, 

 Alabama Experiir.ent Station, Auburn, Alabama 



with contributions by 



LEON JACOBS, Washington, D. C. 



FRANKLIN G. WALLACE, Dept. Zool., Univ. Minnesota, 

 Minneapolis, Minn., and M. B. CHITWOOD, Babylon, 



N. Y. 



Acknowledgements: The writer is especially indebted 

 to Dr. B. G. Chitwood for many helpful suggestions and 

 criticisms. He also wishes to acknotvledge his appreciation 

 to Dean M. J. Funchess and Pi-ofessor J. M. Robin.ton 

 for making facilities a)id time available. Many of the 

 eggs studied were supplied from the collection of the 

 Bureau of Aniinal Industry throitgh the cooperation of 

 Dr. Benjamin Schwartz and other members. Acknowledge- 

 ments are likewise due Dr. Dale A. Porter for materials 

 and reviexving the manuscript, Dr. Harold Mantor, Dr. 

 Wilforu Olsen, Dr. V. N. Moorthy, Dr. Franklin G. 

 Wallace, Eugenia Rutland Moore, and Dr. J. E. Greene, 

 all of whom supplied materials for study. Of considerable 

 value ivere the suggestions and the aid of Alyce Mae 

 Christenson and Mr. Ernest Rouse who assisted on 

 certain aspects of the problem. — K. O. C. 



Layers of the Egg Elnvelope 



HISTORICAL REVIEW 

 R. O. C. 



The history of the development of the egg of nema- 

 todes begins with the classic work of Nelson (1852) on 

 To.vocara cati. Nelson recognized three portions of the 

 genital tube set apart from each other by sphincters, 

 namely: (1) the ovaries, (2) the oviducts, and (3) the 

 uteri which join to form the vagina. He noted that the 

 egg primordia of the extremities of the ovaries enlarged 

 as they passed down the ducts forming the germinal 

 vesicles at the center of which the nucleus or germinal 

 spot was located. The yolk granules were considered to 

 be derived either in the distal portion of the ovary or from 

 the striated part of the ovarian wall near the junction 

 of the oviduct. The vitellus was formed when the con- 

 solidation of the yolk was completed about the germinal 

 vesicle. 



According to Nelson the production of the vitelline 

 membrane and the chitinous shell occurred in the oviducts. 

 Following contact with the wedge-shaped sperm the eggs 

 began to change in form. Almost immediately the 

 chorion (chitinous shell) began to develop, three strata 

 being recognized. The vitelline membrane separates off 

 from the inner stratum when the chitinous shell is com- 

 pleted. Nelson implies that shell production is an en- 

 dogenous process since there is no increase in total 

 diameter of the egg during its development. 



Bi-schoff (1855) criticizes Nelson regarding the pene- 

 tration of the sperm, maintaining that he saw only 

 epithelial cells adhering to the periphery of the vitellus. 

 The diagrammatically clear descriptions of Nelson, how- 

 ever, and his excellent figures, leave no doubt that what 

 he observed were actually the sperm- :ells. 



Meissner (1856) divided the genital tube of the Mermi- 

 thoidea into four parts: (1) the ovary (Eierstock) , (2) 

 the vitellogene (Eiweissschlauch), (3) the tuba, and 

 (4) the uterus. The vitellogene and tuba together 

 correspond in part to the oviduct of Nelson. According 

 to Meissner the eggs "ripened" in the ovary and during 

 the process acquired a membrane which possessed a 

 micropyle for the entrance of sperm. 1 he egg was 

 considered to be intimately related to the rachis as a 

 sort of divei'tijulum which separated off as the eggs 

 entered the vitellogene. In the vitellogene the chorion 



was first produced, and in the vaginal portion the protein 

 coat was described as originating from a clear, droplet 

 containing substance. The byssi, according to Meissner, 

 are produced in the tuba. The uterus was considered 

 to function only as a retention chamber for the eggs. 



Kiichenmeister (1857) described the formation of the 

 ■-horion from a solidifying mass secreted by the walls 

 of the uterus, laid down in constantly thickening layers 

 about the vitelline membrane. Kiichenmeister noted 

 the difference between the appearance of the opercula 

 and the chorion of Trichuris. In Enterobiu.'i vermicularis 

 he described a light hood or cap at one end which he 

 considered as an expression of the fact that the chorion 

 had not been completed. This, in all proba'oility, was 

 the protein coat. 



Cobbold (1864) describes the process of egg formation 

 and membrane production in Ascaris lumbricoides essen- 

 tially as does Nelson {Loc. Git.). The ovarian portion 

 he divided into the ovary and the vitellogene. The union 

 of the sexual elements is innnediately followed by the 

 condensation of the yolk granules which obliterate the 

 germinal vesicle. The ovum assumes an oval shape and 

 the vitelline membrane and chorion form. The chorion 

 finally assumes a regular tuberculated surface. In 

 Trichuris trichiura he describes the abrupt termination 

 of the poles at the end, and projection of a transparent 

 inner membrane to form the opercular papillae. 



Leuckart (1886) states that the eggs of Ascaris lumbri- 

 coides and Trichuris trichiura are thick-shelled, and the 

 former further enveloped in an albuminous sheath usually 

 colored with bile pigment. He describes the polar perfora- 

 tions in the latter species and notes that the opercula 

 are albuminous plugs. 



Blanchard (1889) describes the formation of two 

 layers of the egg envelope after the egg reaches the 

 uterus in Ascaris, the inner being more resistant to 

 pressure and the outer more friable in spite of its great 

 thickness. It is formed of concentric beds indicated 

 by a delicate striation. The egg in the anterior (vaginal) 

 part of the uterus comes into contact with a clear 

 albuminous substance which is deposited over its surface. 

 This substance is at first homogeneous but soon distiib- 

 utes in the form of small, hemispherical tubercles giving 

 the characteristic appearance. The eggs are agglutin- 

 ated together by their albuminous envelopes into a 

 voluminous mass. 



It thus becomes clear that some of the early workers 

 recognized the three primary layers of the egg shell, 

 namely: (1) the vitelline membrane, (2) the chitinous 

 true shell, or chorion, and (3) the protein coat. The 

 protein coat is generally accepted to originate from an 

 exogenous process from the uterine secretion. The en- 

 dogenous origin of the chitinous shell is implied by 

 Nelson. Regarding the origin of the protein coat the 

 general opinion is that it develops from a secretion of 

 the uterus which adheres to the surface of the cuticular 

 shell. 



Ziegler (1895) noted that the eggs of Diplogaster 

 longiciiuda and Rhabditis terricola entered the uterus 

 and within an hour the shell is formed. In the former 

 species he found no centrosome in unfertilized eggs and 

 that the shell did not form. Rauther (1930) points out 



174 



