GROWING LYMPHATICS AND THE MESENCHYME 369 



They may, however, grow thicker as new processes are sent out 

 beyond. This increase in thickness takes place at the expense 

 of other portions of the cell. Thus, while (fig. 13) processes 2, 

 3 and 4 successively increase in thickness, processes 1, 2 and 8 

 decrease. In fig. 13 A, the main body of the cell lies at 1, in fig. 

 13 D, process 1 is merely a short hair-like filament. The mode of 

 progression, then, seems to be a true amoeboid one, since change 

 in position is brought about by the sending out on the one side 

 and the withdrawal on the other of cell processes, with a shifting 

 of the main body of the cell from the retreating to the advanc- 

 ing processes. That the wandering is an active process and not 

 the result of a purely mechanical pulling and pushing, is shown 

 by the character of the changes which the cell undergoes. It 

 is impossible that such changes as are shown in fig. 13 could be 

 produced by a merely mechanical dragging and pushing. 



The rate of progression of the individual cells varies. Wander- 

 ing is most marked in the cells in the interior of the fin, while those 

 near the surface are almost stationary. The former are repre- 

 sented with cross lines in the drawings, the latter are dotted or 

 solid black. The cell B between fig. 2 and fig. 9, two days, wand- 

 ered about 22 micra. Cell G shown in fig. 13, wandered in three 

 days about 44 micra. Roughly speaking since the thicker por- 

 tion of the cell measures from 25 to 30 micra in length, the main 

 body of the cell may wander a distance equal to its own length 

 in two to three days. It is probable that this is rather low for 

 the normal maximal rate, since the prolonged use of chloretone 

 causes a slowing of the growth processes. Moreover, during most 

 of the time over which the observations extended, the weather 

 was unusually cold, which also causes a retardation in growth. 

 Since growth processes are much more rapid in the regenerating 

 than in the normal tail, it is probable that a very much higher rate 

 of wandering may be observed there. 



The direction of wandering is principally toward the free mar- 

 gin of the fin, as may be seen by a glance at fig. 12. During the 

 observations many cells, such as cells 15, 16, 17, moved out into 

 the fin from the space between the muscle layers. A small amount 

 of antero-posterior wandering occurred, as seen in cells H l and 



