578 Transactions of the Society. 



It is easy to imderstand the condition seen for example in 

 Figs. 6 and 7, where the nuclei still remain normally attached to 

 their cell protoplasm which is to form the wall of the future blood- 

 vessel. But what is to become of ff, Fig. 12, when its nucleus 

 floats away ? Will a new cell take its place when the circulation 

 is established, or will the unnucleated protoplasm remain in the 

 same position ? This we are unable to detennine, bnt the varied 

 conditions seen in the different examples we offer lead us to sup- 

 pose that, up to a certain stage, there is an analogy between the 

 physiological and the pathological vacuolation of cells. In the 

 vessel-forming cell, however, the accumulating vacuolar fluid finds 

 an escape into the circulation before much damage is done to it ; 

 but there is no vent for the pathological vacuolar fluid, and it there- 

 fore ends by destroying the cell. 



We have already referred to the appearances sometimes, but not 

 always, seen where a line of elastic fibre marks out the track 

 subsequently to be occupied by a loop of blood-vessel. Such an 

 appearance is shown under a low power at A, Fig. 12, where, 

 however, the tint of the fibres has been purposely exaggerated for 

 the sake of distinctness. It is not our intention to enter into the 

 question of the development of elastic fibres, of which so little that 

 is satisfactory is known at the present day, but rather to inquire 

 into the relation which may exist between them and the cells e, f, h, 

 and y, which lie along the fine of fibre or fibres and represent the only 

 links as yet in the future chain of blood-vessel. After premising 

 that these fibres are only a few of the many elastic fibres which 

 exist at that spot, but which, as they do not interest us at present, 

 we have not drawn, lest they should confuse the appearances, we 

 have first to ask if those fibres existed before the cells placed them- 

 selves upon them, and if so, how was it that fibres came to be 

 placed so exactly in the line of the future blood-vessel ? Were 

 even this answered, are we then to suppose that the cells e, f, g, 

 and h clamber along the fibre from the nodal points a, h, and c, in 

 the existing blood-vessel, in order to place themselves where they 

 are especially wanted ? All these and a host of other questions may 

 be asked on this subject which our present knowledge does not 

 enable us to answer; and we ourselves, after much study and 

 examination of these and analogous appearances, have come to one 

 hypothetical conclusion which seems to apply to them all. 



We do not believe that the fibres existed there before the cells, 

 but we beheve that they were made by the cells as these passed 

 into position ; that just as a slug leaves a trail of slime behind it, 

 those wandering cells may leave a trail behind them of a substance 

 which is known afterwards as elastic fibre, and that this tendency 

 accounts for the infinite shapes, sizes, branches, and positions 

 occupied by such fibres. We distinctly oiler the foregoing merely 



