298 ON SOME TREMATODE PARASITES OF AUSTRALIAN FROGS, 



posterior end, till in the region of the cotylojjhore, both ventral 

 and dorsal surfaces are quite flat. The body is 2-98 mm. long, 

 and 1-007 mm. bioad in front of the disc; the latter is 1 4 mm. 

 broad. The suckers on the disc are fairly circular iji outline, 

 0-268 mm. in diameter, and are arranged round its edge, more or 

 less in a circle. The radial muscles of these suckers are very 

 conspicuously developed. In the centre of each suckt-r, the 

 muscular tissue is perforated by a plug of connective tissue( Fig. 18) 

 which runs through to the surface, and lying in this tissuf-, is a 

 strong bundle of muscle-filn-es, placed at right angles to the 

 surface, the action of which is to draw back the bottom of the 

 sucker in the process of attachment. Four larval booklets are 

 present in a row on the ventral surface near the posterior edge 

 of the disc or cotylophore. The hook resembles a button-hook; 

 the .shaft is bifurcated(Fig.l6). I have been able to find no trace, 

 either in the living worms or in the fixed material, of the larval 

 booklets which P. integerrimum and other species of this genus 

 bear near the anterior edge of the disc. There is a small anchor- 

 shaped hook in the centre of each sucker. All these booklets 

 either disappear as the animal increases in age, or very readily 

 become deta(-hed. In only one out of sixteen specimens have the 

 whole four posterior booklets been present; and in only two others 

 were any booklets at all to be seen. In all the other specimens, 

 no booklets could be made out. But the pair of large chitinou.s 

 hooks, lying between the two most posterior suckers on the ventral 

 surface of the disc, is present These hooks are flat plates dorso- 

 ventrally; but, in surface-view, they have a wide posterior border, 

 which is generally split up by two or three incisions, and the 

 general shape is that of a reaping hook with the point bent sharply 

 back(Fig. la). Just at the bend, the hook bears a bifid, crest- 

 like process. These hooks are 0-15 mm. broad at the base, and 

 have a length, measured in a straight line from the base to the 

 height of the bend, of 0-29 mm., while the recurved, claw-like 

 terminal portion measures 0-05 mm. 



At the sides of the body, near the junction of the first and 

 second body-fourths, the vaginal openings are situated on two 

 well-marked papilla-like elevations. 



