STRUCTURE OF THE CYSTICERCUS CELLULOSE. 97 
muscular fibres, they still continue to grow, especially in 
breadth ; but they lose their cilia, and gradually acquire 
those parts which have been described as belonging to the 
neck. The first, evidence of this addition is the appearance 
of inversion of the middle part of the cyst, forming a small 
hollow, the sides of which look as if thrown into folds con- 
taining granular matter, and the bottom presents a circular 
space in which are granular particles of various forms and 
sizes, but those in the centre are darker than the rest. It is 
from these particles that the suctorial discs, the hooklets, 
and the first of the laminated bodies are about to be formed, 
but as yet none of these parts are recognisable. At a stage a 
little more advanced, this apparent inversion of the cyst has 
increased, the neck has become longer, and the appearance of 
discs, hooklets, and laminated bodies is sufficiently distinct to 
be perfectly recognisable. The process of development is 
particularly apparent in the hooklets, and perhaps there is 
no other instance of the growth of an animal tissue which 
presents such facilities for the examination of the manner in 
which it is effected. First, because the part of the entozoon 
on which these organs are formed, is sufficiently transparent 
to admit of examination by the highest magnifying powers 
without any previous dissection. Secondly, because the 
material of which they are composed is so characteristic, and 
so dissimilar to the surrounding parts, that it can be detected 
in the minutest possible quantities. And, thirdly, as only a 
few of these hooklets are in progress of development at one 
time, and as these are in all stages of formation, every step 
in the progress of their growth can be traced from the merest 
molecule to a perfect hooklet. This is important in reference 
to the general theory of development, as it furnishes an ex- 
ample of the formation of a complete set of organs, on a plan 
more simple, and at variance with the cell-theory of Schwann 
and others. Before one of these hooklets takes on a recog- 
nisable form, it exists as a group of exceedingly refractive 
particles, all apparently of the same composition, and of a 
more or less globular form, but of very different sizes, some 
being so minute as scarcely to be visible by oneeighth of 
an inch lens, others being almost as large as the handle of a 
perfect hooklet, while the rest are of all dimensions between 
these extremes. The next condition of a hooklet is the 
apparent fusion or coalescence of some of these particles into 
the hooked part of the organ. Then the handle and tubercles 
are added, these having been previously formed by the fusion 
of the smaller particles, and these latter by the coalescence 
of the minutest and the minuter ones. Before the several 
