356 ELIOT R. CLARK 



of the fin expansion. The lymphatics ' grow in as outgrowths 

 from the dorsal and ventral longitudinal lymph trunks, and soon 

 catch up to the blood capillaries; from then the two systems are 

 practically coextensive. Careful studies were made of the two 

 sets of vessels, as they developed side by side, and each was 

 found to be quite independent of the other. Blood capillaries were 

 watched through their various transformations. Some were 

 seen to be converted into arterioles or venules as the capillary 

 area increased, while others were watched through the stages of 

 atrophy, solidification and retraction. Neither new nor atrophy- 

 ing blood capillaries contributed tissue to the lymphatics. 



The lymphatics are apparently quite uninfluenced by the blood 

 capillaries. They have a specific independent life of their own. If 

 a capillary is selected and carefully observed, it is found to be in a 

 state of perpetual activity. Fine pointed protoplasmic processes 

 are being continuously sent out at the sides and tip. These proc- 

 esses reach varying lengths and most of them are again withdrawn. 

 The lumen of the capillary may, however, extend into the base 

 of one of these .fine processes, and, gradually extending, lead to 

 an increase in the length of the capillary, or to the formation 

 of a branch. A branch which is at first without a nuclear area, 

 will, if it continues to grow, receive one from the parent stem. 

 That these growth processes are intimately associated with func- 

 tional activity was suggested by the observation that extra vasated 

 red blood cells may be taken into the interior of the capillary, 

 through one of these finely pointed processes. 4 



4 A. Dziurzynski (Untersuchungen iiber die Regeneration derBlut-und Lymph 

 gefasse im Schwanze von Froschlarven, in Extrait du Bulletin des Sciences 

 de Cracovie, serie B: sciences naturelles, March 1911) states, in a footnote, 

 pp. 207-208, that he has failed to observe the taking up of red blood cells by the 

 lymphatic capillaries, although he sought eagerly for it. The accuracy of my 

 observation of this unexpected process is hardly open to doubt. It was seen many 

 times and with perfect clearness, and has been verified in the studies which are 

 to be reported in the present paper, on hyla pickeringii larvae. The illustrations 

 of the various stages, given in my earlier paper, (E. R. Clark, Anatomical Record, 

 vol. II, no. 4, 1909, figs. 6 and 7) are not exaggerated. It must be concluded, then, 

 that for some reason Dziurzynski has missed seeing the process. I am inclined 

 to believe that his failure is due to the crudity of his method of observation. 

 On page 189 he states that his larvae were placed on a slide, with a cover-glass 

 over the tail. Also that he was able to observe a larva for only one, or, at most, 



