WITH NOTES OX THE WEST INDIAN SPECIES. 243 



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. fiava the ciliated grooves show through the skin during life but, as Hill has 

 pointed out, there are no glandless epidermal stripes. 



In Pt. samiensis 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. 



i a i -dal 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," and has since been described by Hill in Pt. hedleyi 

 a- ' 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. flava 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. 



