natural, history

1&, CESTODABYSTEPHEN PRUDHOEDEPARTMENT OF ZOOLOGY, BRITISH MUSEUM (NATURAL HISTORY)During the visit of the Danish Expedition to Rennell Island in 1951, some cestodeswere collected from a Pacific Pigeon (Ducula pacifica pacifica). This material, however,is mainly fragmentary, but appears to be identical with some tapeworms in thecollections of the British Museum (N. H.) from a "pigeon" in the British SolomonIslands, and with the specimens recorded, but not described, by BAYLIS (1926) asRaillietina (R.) insignis (Steudener, 1877), from DucuJa badia in Sarawak.It is upon these three sets of material that the following description is based:Raillietina (Raillietina) insignis (Steudener, 1877)The length of a comp'ete specimen measures up to 130 mm. and in maximum width2 mm. The scolex is readily differentiated from the "neck" and measures 0.22-0.27mm. long and 0.30-0.39 mm. wide. In very contracted specimens, however, the demarcationbetween the scolex and Jhe "neck" is scarcely distinguishable. The rostellum,0.15-0.22 mm. in diameter, is armed with a double crown of about 200 hooks, measuring0.015-0.017 mm. in length. The four suckers are rounded or elliptical and havea diameter of 0.067-0.10 mm. They each bear five or six rows of minute spines. Thereis an unsegmented "neck", which may be somewhat narrower than the scolex, andsegmentation begins at about 0.75 mm. behind the latter, or in contracted specimensat about 0.34 mm. Throughout the strobila the segments are broader than long. Incross-section the longitudinal musculature of the mature segments forms three distinctrings. The muscle-fibres of the inner ring are disposed in relatively thick, welldefinedbundles, while the outer ring consists mainly of individual fibres. Betweenthese two, there is a third ring of fibres aggregated into bundles noticeably moreslender than those of the inner ring. The transverse muscula ture forms a loose layer ofindividual fibres between the cortical and medullary parenchyma. Single dorso-ventralfibres are also present. The ventral excretory canals and their transverse connectionsare wide, but the writer has failed to observe any dorsal canals. Scattered throughoutthe parenchyma, particularly the cortical parenchyma, of specimens from Ducula p.pacifica and the "pigeon" there are numerous well-defined "calcareous bodies".These are more noticable in specimens stained with Ehrlich's haematoxylin than thosestained with Mayer's paracarmine.83