GROWING LYMPHATICS AND THE MESENCHYME 357 



A few observtions were made on the relation between the grow- 

 ing lymphatic and the mesenchyme cell. Here again, as in the 

 case of the blood capillaries, while this point was not subjected 

 to such rigid tests, nothing was seen which would suggest that 

 there is any transfer of tissue from mesenchyme to lymphatic. 



The finding of larvae of hyla pickeringii, during the spring of 

 1910, made possible a new set of studies. The tadpoles of this 

 species offer peculiar advantages over those of rana sylvatica, 

 r. palustris, and r. catesbiana which were previously used. They 

 are smaller and more transparent, are free, for a longer period, 

 from toublesome pigment cells, and are very much easier to 

 anesthetize. But of much more importance was the discovery 

 that, in the posterior portion of the tail, the lymphatics grow 

 into the fin expansion of the tail in advance of the blood vessels. 

 In fact, specimens may be met with in which, over a region cor- 

 responding to the posterior twenty muscle segments, the lym- 

 phatics have grown out in abundance, reaching almost to the 

 fin margin, without a single blood capillary appearing beyond 

 the edge of the central muscle mass (fig. 1). 



The importance of this discovery will be appreciated readily. 

 If, on further investigation, it be found that, in this area, no blood 

 vessel has at any time been present, during the growing out of 

 the lymphatics, the question as to the possibility of the growth 

 of lymphatics independent of blood vessels will be settled. 

 Obviously the only way to be certain is to select a portion of the 

 lymph trunk before the branch has appeared, to watch its growth 

 and see whether there is even a transitory appearance of a blood 

 capillary near it which might contribute to its growth. If it be 

 found that the lymphatics do indeed precede the blood vessels, 



two hours, because of the return of movement. Had I used such a method I feel 

 quite certain that I should also have failed to observe this process, for it was only 

 by the use of the upright chamber, and by the most careful use of the chloretone 

 so that the same larva could be observed for many hours at a time, and over 

 periods of several days, that I made the discovery. Another possible explanation 

 of the divergence of our results may lie in the difference in age of larvae studied. 

 While Dziurzynski does not state the age of the ones used for this particular 

 study, it may be inferred from his paper that he studied much later stages than I. 

 The larvae which I studied were rana catesbiana larvae 8 to 9 mm. long. 



