120 
ME. EAINET ON THE STEHCTTJEE AND DEVELOP3IENT OF THE 
that they could have escaped notice. First, because these parts are of such a size and 
degree of transparency as to admit of examination with the highest powers of the micro- 
scope without the necessity of disarranging them, or disturbing their position by mani- 
pulation. Secondly, because the material of which they are composed is so dissimilar in 
appearance to that forming the adjacent tissue, and so characteristic, that it cannot be 
confounded with the structures in their immediate \icinit)'. Thirdly, because at one 
view, in a favourable specimen, booklets can be seen in every stage of their formation, 
from the first grouping together of the masses of formative particles to the blending of 
them into perfect organs ; and lastly, because it is not as if a mere thread of tissue were 
formed amongst other threads, slightly differing in appearance, as fibres of elastic tissue, 
for instance, in a mass of connective tissue, but the objects referred to are perfect organs, 
which possess an arrangement of parts connected together with order and remarkable 
regularity. So that, under such circumstances, if these organs had been preceded by 
nucleated cells, and the cells had been transformed into booklets, neither these cells in 
th6ir primitive state, nor in theii’ several stages of transformation, could have escaped 
detection. 
The parts next to be noticed are the suckers. Indications of these are 'visible as soon 
as the booklets. They appear as four circular spaces, presenting a granular aspect, about 
the size of perfectly-formed suckers. The two sets of fibres next make their appearance, 
the radiating and circular, which have not at first the sharp outline which they after- 
wards acquire, but still appear obscurely granular. As the tissue of these organs pos- 
sesses nothing characteristic like that of the parts just described, the progressive changes 
which they undergo during the different periods of then: formation can be but imper- 
fectly distinguished ; and hence no further description of them will be necessaiy. 
It has been observed in respect to the two sets of organs above described, that their 
size does not increase materially after once formed ; exactly the reverse is the case in 
reference to the part called the neck, and the quantity, though not the size, of the lami- 
nated bodies, which increase in number as the cavity of the latter increases in size. 
These bodies appear as soon as the booklets and suckers, and they are as large when 
first formed as afterwards, but there are indications of the transverse wrinkles of the neck 
before either booklets or suckers can be distinguished. See Plate XI. fig. 8. Tlie neck 
afterwards continues to grow, so that its relative length in respect to the ventral portion 
is some indication of the age of a Cysticercus. 
It is probable that this part does not arrive at its full size until after it has been pro- 
truded, which I have never seen to be the case in any animalcules occurring in or 
betweeir the muscular fibres, and which perhaps is not effected nntil the entozoa quit 
their confined locality between the muscular fibres, and gain access to the fine sin-face of 
a mucous membrane, there, as physiologists generally believe, to be fiu-ther developed 
into a higher form of entozoon. 
In the preceding observations on the development of the Cysticercus celhilosce, I haie 
confined myself entu'ely to such facts as are so obvious and easy of verification, as to 
