The Histogenesis of Cysticercus pisiformis. 213 



colUs is sig-nificant. He says: "Die obersten zwischen den Haft- 

 scheiben gelegenen Teile der Nervenstränge .... zeigen ein auf 

 Längs- und Querschnitten vollkommen gleiches, äußerst fein granu- 

 liertes Aussehen". In distinction to this granular structure in the 

 upper part of the nervous system, Pintner describes the main nerve 

 cords as possessed of distinct fibrillae, v^hich are coarser in the inner 

 nerve cord and finer in the outer. For further details regarding 

 the structure of these cords, the reader is referred to Pintner's 

 text and figures. 



The method of multiplication of the ganglion cells will be con- 

 sidered under Cytogenesis. But at this point may be considered 

 the question of the origin of these cells. Omitting from the discus- 

 sion for the present the peripheral nerve cells, the origin of the 

 ganglion cells only will be discussed at this point. Do they arise 

 from metamorphosed parenchjmia cells, or de novo from protoplasm 

 elaborated either by the general parenchyma network or by certain 

 definite parenchyma cells? Do they arise in situ or is there a mi- 

 gration of nerve cells relative to other tissues ? Are there any def- 

 inite centers of development? 



I have named here the only possible hypotheses for the origin 

 of the ganglion cells suggested to me by a careful study of many 

 developmental stages of the central nervous system. To any one 

 at all familiar with Cestode histology, it will at once be apparent 

 that direct evidence bearing on these questions is very difficult to 

 secure. This is due chiefly to the similarity in appearance between 

 the nerve and parenchyma cells, and also to the fact that the slight 

 différence between them renders the period of development of the 

 former from the latter comparatively short and hence difficult to follow. 



As shown above the origin of the neuro-muscular cells is un- 

 doubtedly to be traced to a metamorphosis of parenchyma cells in 

 situ. Reasoning then by analogy, one would consider it probable 

 that the ganglion cells whose structure is similar to that of the 

 neuro-muscular cells develop similarly. And I have searched dili- 

 gently to prove that this method of development does occur, but 

 without being able to demonstrate it absolutely. I have thought to 

 find occasional ganglion cells lying on the surface of a nerve cord, 

 which, while sending a nervous process into the latter, have at the 

 same time shown an unquestionable connection with the parenchyma 

 network ; but the difficulty of accurate observation on a point of this 

 character and the consequent uncertainty connected therewith is so 



