CrSTICUECUS CELLULOSE, AS FOUND IN THE MUSCLES OF THE PIO. 115 
defined on the side next the sarcous matter. It soon, however, increases in thickness, 
and afterwards becomes converted into short fibres, which increase in size and distinct- 
ness as the animalcule grows larger. These fibres are peculiar ; there is nothing 
that I am acquainted with analogous to them. They have not the sharp and well-defined 
outhne of true cilia, nor are they pointed like setae, or curled like cirri. They have 
somewhat the nature of white fibrous tissue, their distinctness being impaired by acetic 
acid. They are of different lengths in the same entozoon, and generally longer, though 
not thicker, in the large than in the small ones. Their length averages about 
an inch. 
The most remarkable circumstance connected with them is the great uniformity of 
their arrangement in different Cysticerci. See Plate X. figs. 12 and 13. They cover the 
whole of the outer surface of the investing membrane, and on opposite sides of the same 
entozoon, their form, size, and direction are similar, so that the two halves taken longi- 
tudinally are in this respect symmetrical. If the direction of these fibres be examined 
about midway between the two extremities of one of these animalcules, they will be seen 
to project from the sm'face at right angles with the axis of its body ; but if traced each 
way from this point they ivill be observed gradually to incline to this axis at an angle 
which keeps diminishing as they approach the two extremities, so that the fibres nearest to 
the two ends almost coincide in their direction with that of the axis, and thus correspond 
in their situation to the barbs situated on each side of the extremity of an ordinary 
feather. See Plate X. figs. 12 and 13. 
As the first position of these animals is in the very substance of a primary muscular 
fasciculus (see Plate X. fig. 14), it is obvious that the mechanical action of this apparatus 
wiU be to aid then longitudinal development whilst new cells are in progress of forma- 
tion m then interior. For it is scarcely possible that the muscular fibrillse by which 
they are surrounded, can, when in action, fail by their friction to urge the two extremi- 
ties onwards in opposite directions, whilst at the same time the fibres by which these 
entozoa are covered are in consequence of their direction preventing the separated ends 
from regaining their former position, and thus the two ends being always carried in 
opposite directions without the possibility of a counter movement, a general elongation 
must ensue. This apparatus also, by splitting up the primary fasciculi, will serve a loco- 
motive purpose, and thus enable these animals to reach the cellular intervals between 
the muscular fibres, where their further development will be completed. That such is 
the effect of the fibres in question is evident on a careful inspection of some of the fas- 
ciculi in which these animalcules are contained, in which a separation of the fibrillge can 
be seen to have been produced by the pointed ends of the entozoon ; these fibrillee 
having been ob\iously turned out of their original course, and some directed to one side 
and some to the other. This explanation receives confirmation from the fact of those 
Cysticerci which are developed in the muscular parietes of the heart being of a different 
shape from those formed elsewhere, although their structure in all other respects is 
precisely the same. These Cysticerci^ in the first or vermicular stage of their develop- 
