94 STRUCTURE OF THE CYSTICERCUS CELLULOSE. 
by pressure it may be made to protrude. This part is some- 
times called the neck. Its length varies very much in dif- 
ferent Cysticerci , depending upon their age. It is hollow, 
having strong membranous parietes, wrinkled transversely, 
and composed both of circular and longitudinal fibres. The 
cavity has no visible communication with that of the ventral 
portion. It contains a multitude of small oval laminated 
calcareous bodies, which, when acted upon by acids, effer- 
vesce briskly, and become partially dissolved, leaving only a 
small residue of animal matter. When the neck is pro- 
truded, the extremity farthest from the cyst is seen to pre- 
sent an enlargement, sometimes called the head, on the free 
surface of which there is a quadrangular area, occupied by 
four circular discs and a ring of hooklets. Each angle con- 
tains a disc, and the hooklets are placed in a circle around 
the centre of this space. The suctorial discs are traversed 
each by a passage taking rather a spiral course, and termi- 
nating in the cavity of the neck. The membrane composing 
a disc presents two orders of fibres, circular and radiating. 
The hooklets are generally twenty-six in number, thirteen 
long and as many short, arranged alternately a long and a 
short one. Each consists of a curved portion like a bird’s 
claw, and a straight portion or handle ; and at the junction 
of these two parts there are tubercles, two in the short hook- 
lets, and only one in the long ones. The hooklets are crossed 
by two zones of circular fibres. They are also connected by 
radiating fibres, which occupy the spaces between each ad- 
jacent pair, like the interosseous muscles situated between 
the metacarpal bones and phalanges. The hooklets are dis- 
posed like radii, with their points turned outwards and the 
extremities of their handles inwards, which, not meeting, 
circumscribe a circular space whose centre corresponds to 
that of the quadrangular area before mentioned. At this 
part there is no perforation answering to an oral orifice, but 
here the membrane is simply depressed so as to present a 
conical hollow. By pressure upon the neck, this membrane 
can be made to protrude in the form of a tongue-like process, 
to which the handles of all the hooklets are connected, so 
that when this part in the living animal is made to move, 
the handles of the hooklets will be drawn in with it, and their 
points carried from the entozoon, and thus made to pene- 
trate the part to which it attaches itself. These entozoa are 
chiefly found in the cellular intervals between the muscular 
fibres, contained in an adventitious cyst formed by the con- 
densation of the surrounding tissues. No more than one 
entozoon is ever met with in one cyst. 
