4.S8 Royal Society .— 



animal they arc reflected backwards at a very acute angle, like tlie 

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

 two ends. They become less and less inclined as they ap])roach the 

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

 face. Tlie ajiparatus 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 

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

 primary fasciculus into the spaces between tlie muscular fibres. This 

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

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

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

 entozoon in its development longitudinally. That such is their 

 office will be ajjparent on examining a sufficient number of speci- 

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

 been completely split uj) 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 

 Ci/siicerci are, in this stage of their development, also very short and 

 of a dift'erent 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 

 their age and situation. Those situated about the centre, and form- 

 ing the chief part of its bulk, are collected together into rounded 

 masses, giving to many of the animalcules an obscurely annulose 

 a])pearance. They are of an elliptical, or rather reniform figure. 

 'I'his form, however, is not essential to these cells, but merely re- 

 sults from the circular shape of the masses into which they enter, 

 the convexity of each cell being a part of the outline of its 

 resj)ective mass. These cells contain minute granules, or rather 

 molecules, which are variously disposed in different cells, so as to 

 jtresent a variety of aj)pearances, such as circular spaces, which 

 might be mistaken for nuclei, but which seem rather to be jiro- 

 duced by a deficiency of the cell's contents at these parts, than by 

 any distinct nucleus. The mode of formation of these cells must be 

 examined in the growing parts of the animal, and for this purpose its 

 extreme ends are best adapted. When one of these ends is about 

 to have an addition made to its length, the investing membrane 

 at this part becomes at first very thin, and then disajjijcars. A 

 clear space is next seen, having in some specimens the form of the 

 part which is about to be added to the extremity of the entozoon ; 

 in others it has no defined limit. This space contains, in some 

 cases, nothing but extremely minute molecules, of different 



