572 Transactions of the Societtj. 



Figs. 4, 5, and 6, or at right angles to it, as at a, Figs. 1 and 2, and 

 i, Fig. 12. Strange to say, in tlie latter condition the already- 

 existing blood-vessel or capillary seems always ready to meet such an 

 advance half-way, and will either bend its whole tube, in the case of 

 a capillary, or dimple its cellular wall, in the case of a larger blood- 

 vessel, towards the vessel-forming cell, as seen in the examj)les last 

 named. 



It is also worthy of notice that, when we examine the membrane 

 in the vicinity of such a cell, we find that no other cell is as yet in 

 position to continue the process of development ; that, in short, the 

 solitary vessel-forming cell has specially come to place itself in the 

 most favourable position to enter into the continuation of the vessel 

 peripherally, and acts there until another cell may come and place 

 itself beyond it to continue the process. But the most wonderful 

 instinct of all is seen when a large capillary loop is about to be 

 formed, when several cells are seen placing themselves at considerable 

 distances from each other in the precise line which the future vessel 

 is to occupy. This is well seen in Fig. 12, A, which shows under a 

 power of 100 diameters a plan of such a loop about to be formed 

 between a and h, the nodal points in already formed capillaries, 

 where attachments to the circulation are to be formed. In this 

 loop or chain, independently of the cells at a, h, and c already 

 attached to the capillaries (all the component cells of this chain are 

 drawn separately in the same figure at a much higher power) we 

 have four links formed, three of them consisting as yet of only 

 single cells e, f, and h, and one link g, consisting of three cells, 

 two of which are already vacuolating or hollowing out to form a 

 tube before any connection is made with the comparatively distant 

 blood-vessels. Indeed this, the most advanced link of the chain, is 

 almost equidistant from the nodal points of junction at a and h. It 

 will also be observed that while gig', the cells which specially 

 hollow out to form the tube, join by overlapping their ends, or, in 

 other words, by forming a splice, the third cell g" places itself 

 upon the splice or junction of the cells, and therefore at the 

 weakest point, by way of strengthening the whole. This splicing 

 of cells and application at the point of junction of strengthening 

 cells we have found invariably throughout, as will be seen also in 

 all the other figures. Another point of interest at this spot is the 

 position or presence of a fibre or fibres which seem to connect the 

 cells together and with the nodal points, or, in other words, to 

 mark out the line of the future vessel. 



Let us next consider the action or behaviour of a single cell 

 when about to develop into a blood-vessel, and let us choose, in the 

 first place, a single cell joining itself at right angles to an existing 

 blood-vessel or capillary from what seenls to be a perij)heral direc- 

 tion ; but while we say seems, we do not wish to say that such is 



