Studies on Cysticercoid Histology. VI. Observations on the Fully

JANUARY, 1961] HELMINTIIOLOGICAL SOCIETY 35

Studies on Cysticercoid Histology. VI. Observations on the Fully Developed Cysticercoid of Choanotaenia infundibulum (Cestoda: Cyclophyllidea)* MARIETTA VOGE The life history of the chicken tapeworm Choanotaenia infundibulum has been studied by many workers. One of the earliest studies in this country is that of Guberlet (1916) who experimentally demonstrated that flies could serve as intermediate hosts for this tapeworm. Guberlet based most of his observations of the fully developed Cysticercoid on sectioned material, and described in great detail the structure of the scolex, as well as several of the tissues external to the Cysticercoid cavity. Further observations on the structure of this Cysticercoid have yielded additional information to be presented below. MATERIALS AND METHODS Adults of Choanotaenia infundibulum were obtained from chickens in Honolulu, Hawaii. Gravid proglottids were macerated and fed to flour beetles, Tribolium confusum, which were kept at room temperature. Fully developed and infective cysticercoids were obtained one month after infection. The histologic studies presented here are based on two months old cysticercoids fixed in Zenker's fluid and embedded in paraffin. Sections were cut at 7 microns and stained with Mayer's hemalum, Himes' triple stain, or Mallory's aniline blue stain, as previously reported by Voge (1960). DESCRIPTION The most prominent structure in the Cysticercoid is the scolex, which occupies most of the space of the Cysticercoid body and contains well-defined muscular suckers and the elongate rostellum with hooks (Fig. 1). The musculature of the rostellum and other tissues in the scolex are as described by Guberlet (1916). The relation of the scolex to the tissue immediately surrounding it is similar to that observed in Raillietina cesticillus (Voge, 1960) and Hymenolepis nana (Voge and Heyneman, 1960), Unlike these species, the Cysticercoid of Clioanotaenia contains within the cavity a layer of tissue which, by its structure, could not be differentiated from the tissue immediately surrounding the scolex. In some sections, the posterior portion of the scolex is seen to be connected with this tissue, which therefore probably represents additional "neck" tissue. Thus, the delicate and morphologically distinct tissue lining the cavity in species previously studied is apparently absent in Clioanotaenia. External to the "neck" tissue is a very narrow non-nucleated layer of fibers primarily oriented longitudinally. Using high magnification, one can demonstrate the presence of an additional layer of circular fibers (Fig. 3), at right angles and external to the longitudinal fibers. Both layers stain blue with Mallory's stain. External to the circular fibers is a thick, acellular layer, referred to as the external membrane. In material stained with Mallory's or with Himes' stain, this membrane is seen to consist of two

*From the Department of Infections Diseases, School of Medicine, University of Cali- fornia, Los Angeles. This work was aided by a s;rant CE-1583) from the National Institutes of Health, United States Public Health Service, Bethesda, Maryland. The author wishes to thank Dr. Joseph Alicata, University of Hawaii, Honolulu, for his generous help in the recovery of the strain of Choanotaenia; and Mrs. Nora Liu for tech- nical assistance.

Copyright © 2011, The Helminthological Society of Washington 36 PROCEEDINGS OF THE [VOL. 28, No. 1 separate layers: the internal one appears deep red with Mallory's, and yellow with Himes' stain; the external layer stains a deep blue with Mallory's stain and red with Himes' stain. From the results obtained with Hiines' stain, it is likely that the inner coat consists of protein and the outer coat contains polysaccharide. There is no distinct morphological separation between these two layers. The most superficial layer of the cysticercoid is the hyaline coat. This is a relatively wide, transparent, acellular structure which stains a uniform pale blue with Mallory's stain and red with Himes' stain. In the living material, this coat is very smooth and "slippery." Guberlet (1916) refers to these acellular layers as the cuticle, a term which should not be used for structures outside the cysticercoid cavity. In the cysticercoid of Clioanotaenia separation of the external membrane and the hyaline coat occurs only at the line of demarcation of body and tail (Fig. 2). The external membrane surrounds only the body-part of the cysticercoid; the hyaline coat provides a complete and continuous envelope for the whole cysticercoid. Furthermore, no tissue bridge or connection was noted between the tail and the body of the cysticercoid in any of the sections studied. Only a study of histogenesis could demonstrate when and how this separation"occurs, and whether it is a part of the aging process. As shown in Figure 2, the tail consists of a relatively undifferentiated parenchymatous tissue bordered externally by the hyaline coat. The reason for using the terms "external membrane" and "hyaline coat" in the description of this species, is to draw attention to their similarity to structures in the cysticercoids of Raillietina. In E. cesticillus (Voge, 1960), both the "external membrane" and the "hyaline coat" are present and have comparable structural staining characteristics. Interpretation of these two structures in terms of development and function is difficult; the two may represent only a single structural entity consisting of biochemically differentiated layers. It is of interest that the cysticercoids of both Clioanotaenia and Raillietma differ markedly from Hymenolepis cysticercoids in the structure of the peripheral acellular layers. The two fibrous layers, however, are common to all species studied and probably represent equivalent tissues. In Clioano- taenia the tissues outside the cavity are markedly reduced in size and extent as compared with Eaillietina. Whether this represents a primitive or a specialized trait remains to be determined. LITERATURE CITED GUBERLET, J. E. 1916. Morphology of adult and larval tapeworms from poultry. Trans. Amer. Micr. Soc., 35: '23-44. VOGE, M. 1960. Studies in cysticercoid histology. III. Observations on the fully developed cysticercoid of Raillietina cesticillus (Cestoda: Cyclophyllidea). Proc. Helm. Soc. Wash. 27: 271-274. and D. HEYNEMAN. 1960. Studies in cysticercoid histology. II Obser- vations on the fully developed cysticercoid of Hymenolepis nan a (Cestoda: Cyclophyllidea). Proc. Helm. Soc. Wash., 27: 185-188. Fig. 1. Section of fully-developed cysticercoid of Clioanotaenia infundibulum. Tail not shown. Fig. 2. Section through cysticercoid showing position of tail in relation to scolex. Fig. 3. Organization of fibrous layers, external membrane, and hyaline coat. All drawings made with the aid of a camera lucida. Legend for all figures: cs, cuticle of scolex; cf, circular fibers; em, external membrane; fl, fibrous layer; he, hyaline coat; s, scolex; t, tail.

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