Structure of the Bacillary Band of Trichuris myocastoris

Abstract

The presence of two cell types, hypodermal gland cells and non-glandular hypodermal cells, in the bacillary band of Trichuris myocastoris is established. The non-glandular cell component of the band is greatly reduced when compared to the structure of the bacillary band of Capillaria hepatica described previously. Beta cytomembranes occur on the pseudocoelomic side of apparently both gland and non-glandular cells. The structure of the bacillary band of trichuroid nematodes was the subject of several interpretations until electron microscope studies of this region in Capillaria hepatica by Wright (1963) and in Trichuris muris and T. vulpis by Sheffield (1963) indicated that the region is a modified hypodermal chord containing hypodermal gland cells which appear to open through a complex cuticular pore. In C. hepatica it was evident that two cell types, designated hypodermal gland cells and nonglandular hypodermal cells, occur in this region. However, in the Trichuris species studied, two cell types were not described. This note presents electron micrographs of the bacillary band of Trichuris myocastoris which clearly indicate the presence of non-glandular cells, although they are not as obvious as those in C. hepatica. MATERIALS AND METHODS Specimens of T. myocastoris were removed from the cecum of freshly killed nutria (Myocastor coypu) and fixed whole in 1.2% KMnO4 in 0.9% NaCl at ~4 C for 10 hr. The specimens were dehydrated through cold ethanol, transferred to propylene oxide, and embedded in Araldite 502. Sections stained with lead citrate (Venable and Coggshall, 1965) were examined from several levels through the esophageal region of the worms. Received for publication 23 April 1968. RESULTS AND DISCUSSION The non-glandular cells of the bacillary band of T. myocastoris are greatly reduced in number and extent when compared to those of C. hepatica, and hence are not as easily demonstrated. In this regard, permanganate fixation has been a valuable aid as it selectively stains lipoprotein membranes, thereby clearly delineating cellular limits. The marginal non-glandular cells of the lateral hypodermal chord which gave rise to the interchordal hypodermis are most clearly seen (Fig. 1). Within the bacillary band, the non-glandular cytoplasm is frequently seen only as fine processes between hypodermal gland cells. Occasionally these processes can be traced to a nuclear region within the chord (Fig. 2). The cells resemble the non-glandular cells of the bacillary band of C. hepatica in their compliment of organelles, although their glycogen content is much lower. The non-glandular cells enclose the apical ends of the gland cells so that except for a very small area of some gland cells just at the margin of the pore, the gland cell does not come into contact with cuticle. The most striking feature of non-glandular cells differing from those of C. hepatica is the presence of numerous infoldings of the basal cell membrane (p3 cytomembranes, Sj6strand, 1956)