142 Royal Society : — 



part in the living animal is made to move, the handles of the hook- 

 lets will be drawn in with it, and their points carried from the 

 entozoon, and thus made to penetrate the part to which it attaches 

 itself, lliese entozoa are chiefly found in the cellular intervals 

 between the muscular fibres, contained in an adventitious cyst 

 formed by the condensation of the surrounding tissues. No more 

 than one entozoon is ever met with in one cyst. 



Development of the Cysticercus cellulosae. 



The earliest appearance of the incipient stage of the Cysticercus 

 cellulosae is a fusiform collection of small cells and molecules in the 

 substance of a primary muscular fasciculus, or immediately beneath 

 its sarcolemma. These cells, in this condition of the entozoon, 

 have only an imperfect or partial covering; however, they soon 

 become completely enclosed in a well-defined membrane which is 

 at first homogeneous, but which afterwards, sends out short, 

 slender, projecting fibres, resembling short hairs or cilia. These 

 hair-like fibres, though resembling in some respects cilia, differ 

 from them in being much less sharply defined and less pointed ; 

 however, for convenience sake, I shall speak of them as cilia. 

 Their direction is remarkable. At either extremity of the fusiform 

 animal they are reflected backwards at a very acute angle, like the 

 barbs of a feather, their direction being of course opposite at the 

 two ends. They become less and less inclined as they approach the 

 middle of the body, where they stand out at right angles to the sur- 

 face. The apparatus of cilia- like processes above described is evi- 

 dently designed to give to the entozoon, whilst in this stage of its 

 existence, the power of penetrating between the ultimate muscular 

 fibrillae, and thus to enable it to force its way from the interior of a 

 primary fasciculus into the spaces between the muscular fibres. This 

 will be the effect of the friction of the fibriliae against the cilia, which 

 will allow of motion in one direction only. And as its two ends 

 must move in opposite directions, the cilia wiii also serve to aid the 

 entozoon in its development longitudinally. That such is their 

 ofl[ice will be apparent on examining a sufficient number of speci- 

 mens ; in some of which the primary fasciculi will be seen to have 

 been completely split up by these animals. But the correctness of 

 this inference is more strikingly proved by the influence which the 

 size and arrangement of the primary bundles of muscular fibres 

 have upon the form and dimensions of the entozoa. Thus in the 

 muscular parietes of the heart, where the primary fasciculi are smaller, 

 and, from their frequent interlacing, shorter than in other parts, the 

 cysticerci are, in this stage of their development, also very short and 

 of a different form to those found in other muscles, composed of 

 striped fibre, although in other respects perfectly similar ; and, when 

 completely formed, those taken from the heart cannot be distinguished 

 from those formed in other muscles. The cells which have been 

 alluded to as forming the principal part of the Cysticercus thus far 

 developed, and contained in the investment first described, are all of 

 the same character, differing only in their form and size, according to 



