408 
Tapeworms of Birds 
the opposite half: of these latter, one is placed anteriorly to and a 
little to the exterior of the other, their margins just touching. The 
testes on the pore side and the posterior testes on the other side are 
placed equidistant from and close to the middle line of the proglottis: 
they lie in the same transverse plane. All three testes are within the 
rectangle marked out by the four longitudinal excretory vessels. Owing 
to local contraction, the three lie at times in an almost straight line. 
The vas deferens, after leaving the inner end of the external vesicula 
seminalis, runs a short distance postero-transversely to half-way 
between the anterior and posterior margins of the proglottis, still keeping 
to the dorsal surface. Here it breaks up into three vasa efferentia 
which run to their respective testes. Although this arrangement is 
usually constant, in some cases the vasa efferentia from'the two posterior 
testes unite before joining that from the anterior testis: or those from 
the two testes on the side opposite the genital pore similarly unite first. 
These cases are not very common however. 
Female Organs. The vagina opens on the ventral side of the genital 
sinus close to the opening of the cirrus-sac. At first its diameter is very 
small, but about the transverse level of the outer end of the internal 
vesicula seminalis it widens to twice its former width. From the cirrus- 
sac it proceeds dorsally and slightly anteriorly to the receptaculum 
seminis. This latter is ovoid and situated rather anteriorly in the pore 
half of the proglottis, reaching nearly to the mid-line. It is 0092- 
0-103 mm. long x 0-057-0-069 mm. wide. The ducts from it run 
mostly dorso-ventrally and are confined within the space bounded by 
the two wings of the uterus, yolk-gland and receptacidum seminis. 
They conform to the usual type and need no special mention. The 
ovary is ventral and situhted mid-way between the anterior and posterior 
borders of the proglottis. Laterally it extends nearly to the ventral 
longitudinal excretory vessels. Seen from the dorsal surface it is con¬ 
cave in shape with the cavity directed posteriorly and enclosing the 
compact and spherical yolk-gland. The shell-gland is very diffuse, 
being merely glandular matter surrounding the oviduct: it lies dorsal 
to the yolk-gland. The uterus is at first a narrow slender band dorsal 
to the ovary and in the same transverse plane as its anterior border. 
Later it develops two ventral wings which extend nearly to the posterior 
border of the proglottis and enclose a space containing the female 
genital ducts and the yolk-gland. At this point, its cavity begins to 
be incompletely subdivided by outgrowths from the walls: it extends 
laterally to the longitudinal excretory vessels. According to Clerc, 
