116 
ME. EAIKET ON THE STETJCTUEE AXD DETELOP^klEXT OE THE 
ment, are very short and thick, and of an oval shape. Their locomotive fibres, though 
perfectly demonstrable, are very short, and in many instances impeiTect. See Plate X. 
fig. 15. 
This difference might have been anticipated, considering the close texture of the mus- 
cular fibres of the heart, the absence of any well-formed sarcolemma, and the shortness 
of the fibres occasioned by their frequent interlacement, all which circumstances would 
materially tend to diminish the effect of, as well as the necessity for, the fibres which cover 
the surface of the entozoa, and therefore be unfavourable to their longitudinal development. 
After these Cysticerci have reached the spaces between the muscular fibres, their sub- 
sequent development is the same as in other situations, and the perfect animals formed 
in the heart cannot be distinguished from those formed in other muscles. I may also 
add, that, while in the vermicular stage, the Cysticerci developed in the short muscular 
fibres of the tongue, are of a shape resembling very much those of the heart. 
The investing membrane which has just been described as covered unth cilia, is 
entirely filled with corpuscles, all of one kind, remarkably characteristic, and differing 
only according to their states of development. The perfect cells are best seen in the 
middle of an entozoon, but their mode of formation, and the subsequent changes which 
they undergo, must be examined in those parts which are increasing most rapidly, as in 
the growing ends of an animalcule. 
The first appearance indicative of an increase in the length of an animalcule is a thiti- 
ning of the investing membrane, and a separation or partial detachment of the ciha-like 
fibres at the growing end. Next, a clear space, of the form of the part which is about 
to be added, is perceptible a little in advance of this extremity, apparently the result of 
a very fine membranous protrusion. This contains numerous dark molecules of different 
forms and sizes mixed with granules more or less perfectly spherical: the most perfect of 
these globular bodies are those which are nearest to the perfectly formed part of the 
animalcule. These corpuscles, when completely formed, have a bright oily-looking 
aspect, and a diameter of about of an inch. See Plate X. fig. 8. 
These corpuscles have the appearance of being formed by the coalescence of molecules 
which had existed in the clear space before any corpuscles were apparent, by which they 
are afterwards replaced. After a growing end has become thus filled with these globular 
bodies, the terminal membrane becomes more and more distinct, and the cilia-hke fibres 
are afterwards added, which are generally neither so regularly disposed, nor so distmct 
as on other parts of an entozoon. Next, these corpuscles lose their spherical form and 
become flattened, and lastly, they assume their characteristic elliptical or reniform figure 
before mentioned (see Plate X. fig. 10), which they retain as long as the entozoon remains 
in its primary muscular fasciculus. This shape, however, is not essential to these cor- 
puscles, but merely results from the rounded form of the masses into which they are 
grouped together, each corpuscle, by its convexity, forming a segment of the circular' 
outline of its respective group. These corpuscles contain very fine dark granules, so 
variously disposed in different ones, as to present a variety of appearances, such as 
