384 
A Tri-Radiate Tapeworm 
not corresponding to the external segmentation but occurring much 
more frequently. The arrangement of their ducts is irregular in the 
extreme. The genital organs of the second group lie in arm 1 and in their 
occurrence correspond with the external segmentation. The courses of 
their ducts are quite normal and the general arrangement agrees very 
well with that described for this species. The male and female ducts 
open to the exterior in the normal manner. 
In young segments the three arms are all parenchymatous with no 
spaces, the genital organs being embedded in the parenchyma. More 
posteriorly this begins to be less compact and a space forms at the point 
of intersection of three lines drawn down the centre of each arm parallel 
to its sides. This space increases in diameter until it becomes approxi¬ 
mately circular, with the above-mentioned point of intersection for its 
centre, and occupies almost the whole of the space formed by the 
junction of the three arms (Fig. 7, c. sp.). In this space lie the chief 
male genital ducts of the first group, cirrus, vesiculae seminalae, cirrus- 
pouch, etc., supported by thin strands of tissue which fix them to the 
sides. Posteriorly this space is practically continuous through the 
remainder of the strobila and forms a ready means of communication 
between the different proglottides. Into it, close together, open the 
male and female genital ducts. In the anterior part of the strobila 
where there is no central space, its place being occupied by a compact 
block of parenchyma, these genital ducts have no outlet and end blindly 
in the parenchyma: it is not until this space is developed that the 
ducts become functional. 
It is obvious that for the genital organs of the first group there can 
be no cross-fertilisation, self-fertilisation must be the natural order of 
things. The male and female ducts opening side by side into the 
central space would make it easy for the cirrus to fertilise the vagina 
of the same proglottis. This need not necessarily be the case though. 
The central space passing through the matrix segments would afford a 
ready means of communication between the different proglottides. 
Spermatozoa shed into this passage would wander through it and 
enter any one of several vaginae: there could therefore be cross-fertilisa¬ 
tion between two proglottides. It is certain that fertilisation actually 
occurs. Both male and female organs are well-developed, producing 
mature and apparently normal ova and spermatozoa, and mature and 
developing eggs are present in the uterus. 
