The Histogenesis of Cysticercus pisiformis. 205 



may be seen. This is of interest in connection witli the old mosaic 

 theory of the specific destiny of- individnal cells, for here we find 

 the capillary developing- in quite the wrong place. It has an inter- 

 esting bearing, moreover, on Blochmann's statement quoted below 

 as to "beliebige Parenchymzellen", which statement leads to the in- 

 ference that each cell has a definite fate. 



During the growth of the capillary, occasional thickenings ap- 

 pear on its walls as are shown at d in Fig. 42. The circular thicken- 

 ing of the funnel is a secondary development on its inner wall. 

 The increase in thickness and density of the capillary wall is brought 

 about during development, probably by a fusion and condensation of 

 the parenchyma fibres composing it. 



The formation of the deltoid openings of the capillaries into 

 the excretory ducts may arise either by a splitting of the orginally 

 single connection (Fig. 39), or it is probable, tho there is no direct 

 evidence on this point, that the capillary after its development may, 

 by budding, give rise to a secondary opening into the duct. This 

 is suggested at x, Fig. 35, where a capillary is seen represented as 

 sending out two buds just at the point of its union with the wall 

 of the duct. In the section from which this figure was drawn, it 

 was impossible to trace the capillary thru the wall of the duct 

 which was composed of a great interlacing of parenchyma strands 

 and capillaries. 



Shortly aftei' the appearance of the first flame cells, the be- 

 ginning of the excretory ducts may be observed. These arise as 

 inter-cellular spaces in the parenchyma, which later become enlarged 

 by the growing apart of the parenchyma strands surrounding them. 

 Their walls increase in thickness by the addition of new fibres 

 from surrounding parenchyma as the size of their lumen increases, 

 possibly also by multiplication of those present in their walls from 

 the first. The thickness of the wall, however, varies greatly, depend- 

 ing on the state of distension or contraction of the vessel. The 

 course of the fibres in the ducts is either longitudinal, transverse, 

 or diagonal and the same is true of the muscles which appear in 

 their walls in the course of development, and which are not ar- 

 ranged in any definite layers but are scattered irregularly thru the 

 wall. The development of the excretory ducts is illustrated in 

 Fig. 41. Here one sees not only the developing capillary, c, with 

 its capillary cell, cc, but also two excretory ducts with their anasto- 

 mosis developing in the parenchyma. The lumina of the ducts are 



