J. Johnstone 
375 
transverse section, being slightly flattened dorso-ventrally^ but the more 
terminal segments are vei’y nearly circular in transverse section. The 
genital apertures may usually be seen on the latter ten or so segments. 
They are always lateral in position and may be present on either 
margin of the proglottis but without any regularity as regards the side 
on which they occur. 
Bothridia. The scolex possesses two suckers or bothridia which are 
set at an angle to each other so that their anterior extremities 
approximate (PI. XIX, figs. 2 and 3). They are sessile and their 
thickened rims are usually all that project beyond the surface of the 
axial part of the scolex. Seen en face they are roughly oval in outline 
but present a well-marked notch at their posterior margins and a 
slighter notch at their anterior margins. The suctorial surface is that 
of a cup marked longitudinally by a shallow fossa. The depth of the 
suctorial cup depends entirely upon the degree of contraction of the 
scolex : in PI. XIX, fig. 2 the scolex is represented in the extreme degree 
of contraction, while Text-fig. 3 shows the scolex in a state of almost 
complete relaxation. The marginal parts of the bothridia consist of hard 
parenchymal tissue but the greater portion of the organ is muscular. 
The diameter of the scolex decreases passing back from the bothridia 
and then increases again, so that a swelling is formed and this marks 
the positions of the proboscis bulbs. All this part of the Cestode may 
be regarded as the scolex, or as the scolex and “ head-stalk.” The neck 
is the region immediately posterior to the proboscis bulbs and is 
characterised by lack of segmentation and by relatively undiffer¬ 
entiated tissues. Within it are the excretory canals, the longitudinal 
muscles and the nerve cords, but there are no traces of genital organs. 
Of course there is no sharp distinction between the scolex, neck and the 
anterior segmented part of the strobila. Behind the neck segmentation 
begins, the junctions of the young proglottides being marked by narrow 
transparent lines. Then one begins to see the rudiments of the genital 
organs as cords or blocks of cells. 
1 The terms “dorsal” and “ventral” have not the same precise significance in the 
case of a tapeworm as in the case of a higher animal. The ventral surface is usually 
regarded as that on which the genital aperture is situated, but this is lateral in T. erinaceus 
and one can only fix the ventral surface by a comparison of the relations of the genital 
organs. The bothridia are dorsal and ventral, but I have tried to avoid making any 
distinction between upper and lower surfaces and use the term dorso-ventral to designate 
the diameter at right angles to the diameter—from side to side—which is in the plane in 
which the lateral excretory canals are situated. 
