TREMATODES OF AUSTRALIAN BIRDS. 193 



the "genital sucker" is in the form of a thick horseshoe- 

 shaped band or semi-circular arch of muscle fibres, with 

 the bow of the arch directed forwards. At the posterior 

 end the two limbs give off a number of fibres that run into 

 the circular layer of the ventral sucker. (Text fig. 4). 

 Apparently this does not occur in S. expansus or it has 

 been overlooked by Jagerskiold. 



The function of the "cone-shaped" body may be, as 

 Jagerskiold suggests, to "button" two copulating indi- 

 viduals together ; and this may happen in such a way that 

 the openings of the genital sinus in the two individuals are 

 closely applied together so that the genital sinus of the 

 one acting female at the time becomes filled with sperms 

 from the one acting male. The peristaltic movements of 

 the "vagina," movements which the structure of its 

 muscular walls with its well marked circular and radial 

 fibres shows it well able to perform, would then cause these 

 sperms to pass into the female duct. 



But the formation of these parts suggests another possible 

 explanation to me. The absence of a proper cirrus or penis 

 suggests that the animal is, perhaps, like so many other 

 Trematodes that possess this character, self-fertilized. 

 The "cone-shaped " body is of such a form and size, and so 

 placed, that it would fit pretty accurately into the concavity 

 of that specially well developed semicircular band of muscle 

 fibres at the anterior border of the sinus, thus forming a 

 closed cavity of that spacious depression formed by the 

 combined sinus and ventral sucker (text fig. 5). Into this 

 closed cavity the sperms could be ejected by the ejacu- 

 latory duct, to be taken up in turn by the movements of 

 the vagina. The ovary is fairly large (0*407 x 0*155 mm.) 

 placed with its long axis transverse, just behind the middle 

 of the body. It is divided up into a considerable number 

 of lobes. The ootype, yolk reservoir and transverse yolk 



M— December 6, 1916. 



