AVIAN CESTODES. 869 



to the vagina on the anterior side of it. It does not expand any- 

 Avhere into a vesicula seminalis, but forms a large coiL This coil 

 lies in the neighbourhood of the two water- vascular vessels. 



The vagina opens behind the cirrus-sac and is wider, and with 

 more muscular walls in that section which lies close to the ex- 

 ternal pore than elsewhere. It is this region which receives the 

 ciri-us during the auto-copulation refei'red to above. The tube 

 then becomes finer and passes parallel to the sj)erm-duct, as showfi 

 in text-fig. 144. At about the level of the larger, ventral, water- 

 vascula.r tube it expands into a not very large recejjtaculwm seminis 

 (text-fig. 145), which in fully mature progiottids is gorged with 

 sperm. From this point in fully mature segments the vagina 

 then bends back again and divides into two tubes, one running 

 anteriorly and the other posteriorly. In less fully mature pro- 

 giottids the course of the whole vagina is straight and bat slightly 

 oblique, being nearly parallel to the transverse axis of the body. 

 The shell-gland in such segments is ver}^ plain. 



§ Egg Sacs. 



The egg-containing cavities (which do not, as I think, collec- 

 tively represent a uterus) occur in segments which have already 

 begun to lengthen slightly, although they are still much broader 

 than long. In such segments the ovary and testes are fully 

 mature, but show no signs of degeneration. Several of these egg- 

 holding cavities are displayed in text-fig. 143 (p. 865). They are 

 all small, but not of uniform size; their shape is quite uniformly 

 spherical. There is no regularity of arrangement among them 

 that I can detect; they lie everywhere in the progiottids, even 

 among the bundles of longitudinal muscle-fibres; they thus 

 extend into the cortex, a position which is, however, not unknown 

 in other tapeworms, though it is not common. There is no 

 connection to be observed between adjacent egg-cavities, though 

 they may lie in actual contact : that is to say, there is no question 

 of a. network — the cavities are totally independent in fact and, as 

 I shall point out, probably so in origin. 



Tliese egg-containing cavities, the largest of which are smaller 

 than the testes, are definitely marked off from the parenchyma, in 

 which they lie, by a thickish wall. The cavity which lodges the 

 egg* and the vitelline cells is naturally more apparent in the case 

 of the larger sacs. In the smaller ones the egg and accompanying 

 cells fill up the available space completely or nearly completely. 

 The inference appears to me to be that the cavity is formed later 

 perhaps by the exudation of fluid as well as growth of the peri- 

 phery in a way similar to that of the mammalian Graaffian follicle. 

 On the other hand, the structure of the walls of these egg- 

 containing cavities suggests another interpretation. As already 

 mentioned, they are rather thick and thus very conspicuous : in 



* Occasionally two eajfrs are found in the same cavity. 



