J. Johnstone 
405 
Leuckart the “ Befruchtungscanal.” In Tetrarhijnchus and some other 
Cestodes this canal opens into a wide sac—the uterus—but in such 
more primitive forms as Bothriocephalus the uterus begins immediately 
behind the shell gland, and tljere is no distinction between uterine canal 
and the uterus proper. Probably we may regard the differentiation 
into a narrow uterine canal and a relatively capacious uterine sac as 
dependent on the shape, size, and number of the proglottides. In such 
forms as Bothriocephalus there are a great number of segments and 
these are relatively small; whereas in the Tetrarhynchids the number of 
proglottides is small but the individual segments are, relatively to the 
strobila, much larger than in a Bothriocephalus, and are elongated in the 
longitudinal direction; while the ovary and other organs are concen¬ 
trated in the posterior part of the segment. The whole female tract is 
probably morphologically one, but the uterine part becomes greatly 
expanded in the anterior part of the proglottis as the testes degenerate; 
while the posterior tracts must remain narrow because of the crowding 
of the other organs. It is purely for convenience that we speak of the 
posterior convoluted section of the female tract as the uterine canal, and 
the anterior section as the uterus. 
The uterine tract, then, may be said to begin immediately after the 
opening of the vitelline duct. Its wall here has a very similar structure 
to that of the pi’oximal part of the oviduct; that is it has a basement 
membrane with irregular layers of nuclei on inner and outer surfaces. 
Distal to the entrance of the vitelline duct the wall changes in character 
and consists solely of the structureless basement membrane, with some 
superadded fibrous tissue, and with adhering nuclei. The uterine canal is 
thrown into numerous convolutions which occupy the middle parts of 
the proglottis. Its most proximal part contains ova practically identical 
with those present in the ovary, and immediately beyond the opening 
of the vitelline duct these are mixed with yolk cells and these two 
kinds of cells lie together. Soon, however, the yolk cells break down, 
and the ova become yolked and acquire outer membranes. 
The uterus. (Pis. XXI and XXIV, figs. 10 and 11.) The shape and 
dimensions of this structure are diagnostic of the stage of maturity of 
the proglottis; and it is represented in Pis. XXI and XXIV, figs. 10 and 
11 in the immature and mature conditions. In the very youngest 
segments in which it can be recognised it is present as a simple cord of 
cells, which later on acquires a lumen; and still later it becomes a 
thick-walled tube (Text-fig. 8). So long as the testes are developing, or 
contain many spermatozoa, they occupy the greater part of the proglottis 
