Volume 3

Zoological results based on material from New Britain, New Guinea, Loyalty islands and elsewhere / collected during the years 1895, 1896 and 1897 by Arthur Willey.

  • Willey, Arthur, 1867-1942.
Date:
1898-1902
Catalogue details

Licence: In copyright

Credit: Zoological results based on material from New Britain, New Guinea, Loyalty islands and elsewhere / collected during the years 1895, 1896 and 1897 by Arthur Willey. Source: Wellcome Collection.

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    Sometimes the continuity of the grooves appears to be lost or obscured in the interval between two sacculations. The covering-pad is especially prominent in the sacculations, and less so in the intervening tracts. A similar sacculation of the ciliated grooves has been described by Spengel in Pt. erythraea (Mon. p. 183), where it gives rise to special nodal prominences of the body- wall external to the liver-saccules. These nodal prominences are continued behind the hepatic region. In Pt. minuta [where there is a ciliated groove on the left side only (Spengel)], Pt. australiensis Hill and Pt. hedleyi Hill, the ciliated grooves lie close to the epidermis, and corresponding with each groove there is a longitudinal epidermal band characterised by the absence of gland-cells. In Pt. jiava the ciliated grooves show through the skin during life but, as Hill has pointed out, there are no glandless epidermal stripes. In Pt. sarniensis Spengel has described a ciliated groove (Wimperapparat) on the left side only, which however has no relation to, and in fact is far removed from the vicinity of, the epidermis. Caudal Region. This region is above all characterised by the presence of a longitudinal, solid, sup- porting band, derived from and in continuity with the epithelium forming the median ventral portion of the gut-wall. This is what I propose to call the pygochord. It is probably of some economic importance to the animal as it is of diagnostic importance to us. This structure was first described by Spengel in Pt. minuta as a remarkable “ kiel- formiger Fortsatz des Darmepithels,” aud has since been described by Hill in Pt. hedleyi as “ a long and high keel-like process, the slightly enlarged ventral end of which overlies the minute ventral vessel.” In Pt. Jiava it commences at the anterior end of the caudal region as a simple thickening of the ventral wall of the hind-gut which is soon drawn out into a flattened band with dilated distal (ventral) border (PI. XXIX. Fig. 15 6). As a rule the pygochord retains its connection with the gut-epithelium, but at irregular intervals the basement- membrane is continued across the line of junction so as to completely separate the pygochordal tissue from the wall of the gut. The dilated distal end is sometimes similarly shut off from the rest of the band, and the band itself is sometimes con- stricted by transverse fusions of the basement-membrane. Sometimes the band presents a remarkable moniliform appearance due to this fusion of the basement-membrane at different levels (PI. XXIX. Fig. 15 a). The pygochord ceases at the anus. The hind-gut of Pt. Jiava is surrounded by a very feeble muscularis, while the anus is provided with a light sphincter formed by the circular muscles of the body-wall.