342 THE DEVELOPMENT OF CESTODES. 



fibres. Near the cuticle the cells at first retain their original nature ; 

 but after the formation of the head they also change, stretching them- 

 selves out, and finally becoming for the most part the subcuticular 

 spindle-cells which we have already studied. 



As to the arrangement of the muscle fibres, they are most easily 

 understood by reference to later stages. One can distinguish two 

 kinds of fibres thicker and thinner. The former lie deeper, and are 

 grouped together internally to the cortex as a loose, much interrupted 

 sheath. The fibrils, on the other hand, form a network with cubical 

 meshes, which penetrates the cortex and becomes connected with 

 the processes of the subcuticula. It is, however, doubtful whether 

 these two kinds of fibres form two distinct systems, for the thicker 

 fibres not only split and branch, but are at many places directly 

 continued into the network of fibrils. 



While the differentiation of the cortical layer is progressing, the 

 young cystic worm begins to excrete that watery fluid, whose presence 

 has originated the name " bladder- worm," and given occasion to the 

 theory of " dropsical " worms. I am not able to express a decided 

 opinion as to the exact nature of this process, to say whether it results 

 from the flowing together of the interstitial cells, or from the accumu- 

 lation of the lymph among the parenchyma ; yet from my observations 

 of Cysticercus pisiformis I am inclined to adopt the former theory. 

 This bladder-worm differs from its allies in this, that it is only at a 

 subsequent stage, when about four weeks old and from 4 to 5 mm. 

 long, that it becomes a true bladder- worm. Till then it is wholly 

 parenchymatous, filled internally with a mucous tissue, with large 

 vesicles, which is hardly at all sharply distinguished from the cortical 

 layer, but is, like it, penetrated in various directions by muscular 

 fibres. In this form I was able to convince myself that the fluid first 

 collected in vacuole-like spaces, which became ever more distended, 

 and finally flowed together. The interstitial tissue was, of course, 

 thereby destroyed, so that one could often observe how the muscular 

 fibres projected more or less into the water-tilled space, either freely 

 or with attached shreds. 



An indirect proof of the correctness of this theory is also, I think, 

 to be found in the fact that in the ordinary Cysticerci, where the ex- 

 cretion takes place very early (in some when they hardly measure 

 0*3 mm.), and is much more copious than in Cysticercus pisiformis, the 

 bladder-like body consists solely of the above-described cortical layer. 

 The accumulation of fluid has therefore gone on at the expense of 

 the former internal substance. A specially formed border sheath is 

 in such cases wanting, the inner surface of the subcuticular connec- 

 tive substance being itself directly washed by the fluid. 



