378 
Tetrarhynchus erinaceus 
D. Long, very slender spines about 0'06 mm. in length. Their 
bases are only slightly expanded and the spines themselves are very 
nearly straight. There are two of these spines in each series, one 
adjacent to each of the hooks C. 
E. Small, slightly curved spines about O'Ol to 0'02 mm. in length. 
These spines are rather variable both in size and shape. Sometimes 
they are relatively long and resemble the spines D. Such are those 
found in the region beneath the large spines B to D where they are 
arranged in two rows of about six in each. Other spines are short and 
have broad bases being rather like the large hooks A except that they 
are very much smaller and not so strongly bent. In profile they are as 
represented in E, fig. 9. These spines are arranged in a continuous 
longitudinal series of several rows between the two spines D. 
In all these spines the curvature is outward and backward. All 
are hollow with openings at their bases. There does not appear to be 
any mechanism for their regeneration. Their general arrangement is 
represented in the following table where size of the letters represents 
roughly the relative sizes of the spines. 
ll'B c BAAB c DeII 
EEE EEEE. EEEE EE 
The Musculature of the Scolex. The muscles of the scolex may be 
arranged in three main categories: (1) the complex musculature of the 
bothridia; (2) the extrinsic muscles of the proboscides; and (3) the 
intrinsic muscles of the proboscis. Both bothridia and proboscides are 
organs of locomotion rather than of attachment. The Cestode is always 
situated in the large intestine of the host behind the folds of the spiral 
valve, and thus in such a situation that it is not likely to become 
detached by the movement of food matter passing through the intestine. 
Therefore it is generally very lightly attached and can easily be removed 
without injury to the tissues of the scolex. The bothridia are used to 
enable the worm to execute creeping movements on the wall of the 
intestine in the manner already described. The proboscides appear to 
be used for the .same purpose; first of all the organ is extruded and the 
hooks adhere to the intestine. It is then invaginated and the scolex is 
thus drawn forward. Both the bothridia and proboscides are therefore 
very mobile and have a rich muscular supply. 
