DEVELOPMENT OF CTSTICEKCUS. 429 



of different sizes in the substance of a primary fasciculus of a muscular 

 fibre, or between its sarcolemma and the sarcous elements. 



" Though such a collection of corpuscles has a moderately definite shape, 

 being somewhat fusiform, yet it has not a complete investment. It soon, 

 however, acquires a very distinct membranous covering, which is first 

 apparent about its middle, and afterwards at its extremities. Its dimen- 

 sions in this stage of its formation may be about y^^-th of an inch in length, 

 and -nr 1 n nth in breadth, but these are by no means regular. The ex- 

 ternal investment at first appears only as a bright line ol homogeneous 

 substance, best defined on the side next the sarcous matter. It soon, 

 however, increases in thickness, and afterwards becomes converted into 

 short fibres, which increase in size and distinctness as the animalcule 

 grows larger. These fibres are peculiar ; there is nothing that I am 

 acquainted with analogous to them. They have not the sharp and well- 

 defined outline of true cilia, nor are they pointed like setae, or curled like 

 cirri. They have somewhat the nature of white fibrous tissue, their dis- 

 tinctness being impaired by acetic acid. They are of different lengths 

 in the same entozoon, and generally longer, though not thicker, in 

 the large than in the small ones. Their length averages about ^tVo^ °f 

 an inch. 



" The most remarkable circumstance connected with them is the great 

 uniformity of their arrangement in different Cysticerci. They cover the 

 whole of the outer surface of the investing membrane, and on opposite 

 sides of the same entozoon, their form, size, and direction are similar, so 

 that the two halves taken longitudinally are in this respect symmetrical. 

 If the direction of these fibres be examined about midway between the 

 two extremities of one of these animalcules, they will be seen to project 

 from the surface at right angles with the axis of its body ; but if traced 

 each way from this point they will be observed gradually to incline to this 

 axis at an angle which keeps diminishing as they approach the two extre- 

 mities, so that the fibres nearest to the two ends almost coincide in their 

 direction with that of the axis, and thus correspond in their situation to 

 the barbs situated on each side of the extremity of an ordinary feather. 



" As the first position of these animals is in the very substance of a 

 primary muscular fasciculus, it is obvious that the mechanical action of 

 this apparatus will be to aid their longitudinal development whilst new 

 cells are in progress of formation in their interior. For it is scarcely 

 possible that the muscular fibrillar by which they are surrounded, can, 

 when in action, fail by their friction to urge the two extremities onwards 

 in opposite directions, whilst at the same time the fibres by which these 

 entozoa are covered are in consequence of their direction preventing the 

 separated ends from regaining their former position, and thus the two 

 ends being always carried in opposite directions without the possibility 

 of a counter movement, a general elongation must ensue. This apparatus 

 also, by splitting up the primary fasciculi, will serve a locomotive purpose 

 and thus enable these animals to reach the cellular intervals between the 

 muscular fibres, where their further development will be completed. That 

 such is the effect of the fibres in question is evident on a careful inspection 

 of some of the fasciculi in which these animalcules are contained, in 

 which a separation of the fibrillar can be seen to have been produced by 

 the pointed ends of the entozoon ; these fibrilhe having been obviously 

 turned out of their original course, and some directed to one side and 



