358 



ELIOT R. CLARK 



such a region offers an unparalled opportunity to study the rela- 

 tion between the growing lymphatic and the growing mesenchyme 

 cell. 



It seemed that both these points could well be taken up in 

 one set of observations, for it is easily possible, while making a 

 study of the growth of a lymphatic sprout from its very beginning, 

 to note the presence or absence of a blood capillary in the neigh- 

 borhood. 



Fig. 1 Posterior half of tail of hyla pickeringi larva, showing region in which 

 the lymphatics precede the blood vessels. This larva is the one on which the 

 studies shown in figs. 2 to 14 were made. This drawing was made from the living 

 larva on June 3, at the close of the observations. Lymphatics are in solid black, 

 blood vessels in lines. The ventral caudal lymph trunk and a short stretch of the 

 dorsal caudal lymph trunk are shown. A, the lymphatic sprout shown in figs. 

 2 to 14. The larva is shown in this figure in its normal position. In the other 

 drawings the structures are shown in their reverse position, as seen under the 

 microscope. Enlargement 25 times. 



It is most convenient to anticipate results at this point enough 

 to say that during the series of studies to be recorded, no blood 

 vessel entered the region under observation. 



In order to discover the exact relationship which the lymphatic 

 endothelium and the mesenchyme cell bear to one another during 

 their growth, it is first necessary to find out just how each one 

 develops by itself, and then to study the relations between them 

 when they develop side by side. For the mesenchyme cell, a 

 separate study of the observable growth changes is easily possible, 



