The Histogenesis of Cysticercus pisiformis. 201 



e) Excretory System. 



The rudiments of the excretory system first appear at about 

 the time of the appearance of the scolex rudiment. The flame cells 

 are a little in advance of the ducts in point of time of development. 

 The development of this system will be considered under three 

 heads: a) flame cells; b) capillaries; and c) excretory ducts. 



The flame cells originate in parenchyma cells, 

 which, previous to their transformation, are not 

 distinguishable in any way from the other cells of the 

 parenchyma and which remain permanently in con- 

 tinuity with the latter. The first evidence of their trans- 

 formation is the appearance of a single small, narrow, conical, 

 darkly staining body in the cytoplasm (Figs. 29 and 32), or of two 

 bodies one of which is cone-, the other lens-shaped, as in Figs. 21 

 and 37. Considerable variation exists in the relation of these bodies 

 or bodj^ to the nucleus of the cell. When there is but one of them, 

 it may be partly included in the nucleus (Figs. 23, 32), or it may 

 be simply in close apposition with the latter, but not demonstrably 

 in union with it, as in Figs. 29 and 30. When two such bodies 

 are found they may both lie entirely outside the nucleus (Figs. 21, 37), 

 or one of them may be represented by a large chromatin granule 

 lying within the nucleus while the other lies outside (Fig. 28). What 

 is the probable significance of the fact that in some cases one finds 

 two bodies in the developing flame cell, while in others there is 

 but one? The former case may be interpreted as presenting a 

 separation between basal plate and ciliate process as is seen in 

 an adult cell in Fig. 24, while in the latter case they are at least 

 in intimate contact, if not in protoplasmic continuity with each 

 other. The latter is the condition met with typically in adult 

 cells (Fig. 20). In the case of those developing cells whose basal 

 plate and ciliate process are separate, it is possible that a later fusion, 

 or at least apposition, of the two occurs. They may, however, 

 remain separate in the adult condition. Such a separation of basal 

 plate and ciliate process has been described by Pextnee (1896). 

 What is the source from which these, the basal plate and ciliate 

 process are derived? The evidence at hand indicates very strongly 

 that it is the chromatin. In Fig. 28 is found a large chromatin 

 mass situated in the nucleus close to the base of the ciliate process 

 and strongly suggestive in its appearance and position of the basal 



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