The Histogenesis of C3'sticercus pisiformis. 221 



the extreme difficulty of difFerentiating' these elements from those of 

 the parenchyma in which they are imbedded, and the intimate 

 intermiug'ling of these two tissues with one another. Another source 

 of uncertainty is probably to be found in developmental and 

 physiological diiferences, to which point reference will be made 

 later. Regarding- the origin of the neuro-muscular cells in Tetra- 

 rhynclius longicollis Pintnek (1880, p. 66) saj^s, that "... sie aus 

 den embryonal artig indifferenten Parenchymzellen entstanden . . .", 

 The "ganglion cells" have been described as varying, not only in 

 size, apart from the differences in size which are to be expected in 

 different species, but also in polaritj^ shape, structure of cytoplasm 

 and nucleus, number of "nucleoli", possession or lack of cell mem- 

 branes, etc. 



Such a distinction as Apathy (1897) makes between ganglion 

 and nerve cells cannot be seen in Cysticercus pisiformis, if, 

 indeed, it exists in any other Cestode. 



For a full discussion of the different views regarding the conducting 

 element of the nervous system, the reader is referred to Cohn (1898, 

 136 and 138 — 43). As additional evidence to that given by Cohn 

 (1898) and Apathy (1897) in favor of the view that the conducting 

 element is fibrillar and not interfibrillar in character, may be added 

 the observation that the granular cytoplasm in the cephalic ganglia 

 and also at different places in the main nerve trunks may be seen 

 differentiating itself into fibres and the same is true of the cyto- 

 plasm of the cell bodies themselves. ^) This cytoplasma is un- 

 questionably neurogenic in function, composing as it does the great 

 bulk of the cephalic ganglia, and therefore the fibres developed from 

 it must be nervous elements. 



The views of Niemiec (1886). Zeexecke (1895) and Cohn (1898) 

 regarding the conducting element may be considered briefly at this 

 point. These three, as indeed most authors, are agreed that this 

 is fibrillar in character, but they differ as to whether this element 

 is found in the meshes of the network composing the nerve cords, or 

 whether there are specialized fibres running thru and among the 

 latter. The former view is held by Niemiec and Zernecke, the 

 latter by Cohn. The two former authors differ, however, as to 

 whether an}' portion of the network is composed of parenchyma 



1) No distinction can be made at this stage between fibres and 

 fibrillae. 



