neio Genus of Avian Ceslodes. 417 



Genital Oi'jans. — There is a sinole set of botli male and 

 femnlo or<^ans in each mature sef];mcnt. 



The testes number (JO or more. Tliey are rounded and 

 have a diameter of about 0*05 mm. They lie closely together 

 throughout tiie medulhiry parenchyma, occupying practically 

 the whole of the space in all directions which is not taken up 

 by the ducts and female organs. 



The vas deferens is a wide, very closely coiled tube, 

 running out from near the centre of the segment, over the 

 loTigitutlinal excretory canal, to enter an elongated cirrus-sac, 

 which tinally opens into tlie genital atrium. It is a curious 

 fact that just before entering the cirrus-sac the vas deferens 

 narrows suddenly to one-tenth of its previous diameter 

 (0*0025 mm., as compared with 0*025 mm.). 



The cirrus-sac is small ajid somewhat elongated. It is 

 broadest at its inner end (which measures 0*042 mm. across), 

 and tapers gradually towards its external opening. The 

 sac lies just lateral to the longitudinal excretory vessel. 



The ovary is a compact organ, more or less oval, but with 

 a somewhat irregular outline. It lies towards the hinder 

 part of the segment, in the ventral region, and is surrounded 

 in almost all directions by portions of the uterus. 



The vagina opens into the genital atrium immediately 

 behind the cirrus-sac, in the same horizontal plane. From 

 its opening it runs inwards with a sliglit backward inclination 

 at tirst, then quickly bends so as to run parallel with the 

 cirrus-sac. On passing internally to the excretory vessel it 

 begins to widen out gradually, and forms a little bulbous 

 expansion, after which it again becomes a very narrow duct, 

 and almost at once runs into an oval receptaculum semiuis 

 at about the level of the innermost coils of the vas deferens. 

 Between this point and the ovary there is a considerably 

 coiled oviduct. The vagina is lined thickly, from near its 

 external opening until it begins to widen, with stout cilia, 

 of which a peculiar feature is that they appear to be deeply 

 stained by hajmatoxylin. They all have their free ends 

 pointed outwards, towards the external opening of the duct. 



The uterus is a large saccular organ lying in the ventral 

 and posterior portions of the segment, and extending round 

 and between the other organs wherever it can find room. It 

 seems at first to be subdivided into a number of more or less 

 separate lobes or compartments, containing more or fewer 

 eggs. It is also almost completely divided into tvvo portions 

 by the vas deferens, which presses it down on to the ventral 

 side, so that only a narrow uterine space (just wide enough 



