GROWING LYMPHATICS AND THE MESENCHYME 373 



form and the characteristic power of amoeboid movement of the 

 non-dividing - mesenchyme cell. There was nothing whatever to 

 indicate that either the non-dividing or the dividing mesenchyme 

 cell may give off, by bodily transformation or by budding, a leuco- 

 cyte or a lymphatic endothelial cell. The mesenchyme cell, then, 

 during this period of growth, has a specific, independent life. 



Let us now turn our attention to the growing lymphatic. To 

 former observations, which have been confirmed in the present 

 study, some new observations have been added which make the 

 story more complete. The newer work has been concerned par- 

 ticularly with a more careful study of the nuclear areas. 



The nuclear areas occur at somewhat irregular intervals along 

 the wall. When seen in profile, they consist of a thick clear cen- 

 tral portion, surrounded by a granular zone, which extends for 

 a considerable distance longitudinally along the lymphatic in 

 both directions — gradually growing thinner. The term nuclear 

 area is used because the nucleus which may be clearly seen by 

 fixation and staining, merges imperceptibly into the perinuclear 

 area in the living larva (fig. 15). When seen en face the clear 

 central portion is invisible, but the position of the nuclear area 

 is clearly indicated by the granules surrounding the nucleus, so 

 that it is possible to keep track of all the nuclear areas in a sprout. 



If a study is made of the behavior of the nuclear areas it is 

 found that there are two distinct processes going on, wandering 

 and mitotic division. These will be taken up separately. 



The newly formed sprout receives its first nuclear area from the 

 parent stem by an in-wandering along the wall. As the branch 

 grows, it may receive a second and a third nuclear area from the 

 the main stem. How many may wander into a branch cannot 

 be stated; I have watched as many as five pass into a branch, 

 (cf. fig. 16, nuclei 4, 5, 6 and 7). Once in the branch they do not 

 remain at rest, for they are continually moving up or down the 

 lymphatic, or from side to side, along a spiral course (fig. 16). 

 They have a tendency to arrange themselves in pairs on opposite 

 sides of the lymphatic (fig. 16, nuclei 3 and 4)- They may how- 

 ever remain single, or from groups of three or four. In one in- 

 stance, in a sprout which was under observation, four nuclear 



