STUDIES ON THE ECTOPARASITIC TREMATODES OF JAPAN. 33 



In most species of tliis genus described in tin's pajKT, tlic invest- 

 ing inenihnine of tlie suckers is exactly simihjr to that of the other 

 parts of the Ijody ; ]jut in 2V/.s/. ovale the ventral (concave) surface is 

 raised into numerous conical papillae, at the top of Avhicli open the 

 efferent ducts of the numerous unicellular glands after-wards to he de- 

 scribed. Along the inner border of the suckers also there are, in tiiis 

 species, numerous larger papillae crowded together (PI. XXIII, fig. 5). 



rosten'or .suclicr — The posterior sucker of Tristoimun is more or less 

 hemispherical in f(jrm, and is ^'ery similar in structure to thtit of 

 Calicotyle. In most species, however, a short stalk ma}^ be dis- 

 tinguished (PI. XX, fig. 5). The ventral (concave) surface is divided, 

 as in Calicotjjic, by radiating elevations into a central and seven 

 peripheral polygons that surround the fermier ; the hindmost of the 

 peripheral polygons invari;il)ly occupying the median line. In some 

 species (Ti: sinuatum and Tr. rotundinn), the central area forms a reguhu' 

 heptagon ; but in the majority of the species studied by me, its form is 

 that of a heptagon to one side of which an isosceles trapezoid has been 

 apposed by the shorter one of the two parallel sides and with the 

 boundary line between tlie two blotted out (Tr. ovale, Tr.foliaceuiii, Tr. 

 Xoiaivœ, Tr. hiparasitieum). In Tr. siiiuatum the two radial sides of 

 the liindmost peripheral area bifurcate near their outer ends and 

 there form with the margin of the sucker each a small triangle (PI. 

 XX, fig. 1). 



A marginal membrane is always present, and is thrown into 

 wavy folds ; so that in a- surface view, it seems as if it consisted of 

 numerous rectangular portions. Its investing membrane is very thin, 

 and its substance consists of n syncytium Avith its nuclei irregularly 

 scattered, and traversed by niunerous fine, transverse, muscul-u- fibres 

 (PL XXIIT, fig. 3). 



According to my observations on Tr. sinuafinu, the species to 



