AVIAN CESTODES, 597 



coiled within the sac. The cirrus, with which it is continuovis, 

 appears to run a straight course and not to be coiled, since it is 

 shorter than the cirrus-sac. In some posterior segments the 

 cirrus-sac presented a different appearance. The peripheral and 

 greater part of the cirrus-sac is thicker-walled than a terminal 

 rather spherical and wider region into which opens the vas 

 deferens. 



The cirrus-sac is ensheathed externally by a layer of rather 

 large nucleated hyaline cells, a not unu,sual character. 



Did these two forms of the cirrus-sac occur in .different 

 individuals, one would be tempted to see in them a specific 

 diff"erence. 



The vas deferens presents an extensive coil after it issues 

 from the cirrus- sac. This occupies quite one-third of the dia- 

 meter of the segment when the latter is stretched laterally. 

 The coils are at least mainly dorso-ventral in direction, since in 

 horizontal sections the sperm-duct appears as a series of circular 

 transversely cut areas. 



The vagina has a straight or at most slightly sinuous course 

 back to rather beyond the water-vascular tube — this section 

 being thick- walled with a narrow lumen as in so many other 

 Cestodes. A little way to the inside of the water-vascular tube 

 the vagina narrows into an excessively fine bore, though with 

 equally thick muscular walls at first. This slender region is 

 coiled on the horizontal plane. It opens into the receptaculum 

 seminis, which is rather pear-s-haped. This and the succeeding 

 portion of the vagina is nat thick -walled but has a wider lumen, 

 less of course in the case of the vagina. Although the proglottids, 

 in which the vagina and its subdivisions had the characters that 

 have just been mentioned, were not fully mature, at any rate as 

 far as concerns the testes and sperm-duct, the receptaculum 

 contained spermatozoa. It is necessary to point out that there 

 is nothing to be specially remarked upon in the structure of the 

 female efferent duct, which is constructed upon the plan usual 

 in tapeworms. It is important, however, to be accurate, since 

 there are minor differences to be noted which affect even the 

 different species of Davainea. 



Without attempting any general resume for comparative 

 purposes, I may direct attention to one or two species which 

 differ from tha.t now under conaidei-ation in these matters. In 

 D. sj)]iecotheridis of Johnston * thei-e is apparently no distinct 

 receptaculum seminis at all. In D. corvina Fuhrmann T the 

 position of the receptaculum is different, beginning as it does 

 to the outside of the water-vascular tube. In D. polycalceola % 

 the small receptaculum is close to the ovary. It is of further 

 importance to note the age of the proglottid when giving the 



* T. Harvey Johnston, '"Second Report on the Cestoda and Acanthocepluilii 

 collected in Greenland." Ann. Trop. Med. Parasit. iii. 1914, p. 107. 



t Abh. Senck. Nat. Ges. xxxiv. 1911, p. 252, tig. 3. 



X V. .Janicki, " Ueber zwei neue Arten .... Davainea,'' Arch, de Parasit. vi. 

 1902, p. 265, iig. 5. 



