LYMPHATICS IN FROG LARVAE 39 



The results described also represent the essential features of 

 Hover's views of the same date, confirming and extending his 

 claim for toads, which he studied as well as other Anura, that 

 the first lymphatics to appear are the anterior lymph hearts, 

 and that the distribution of the lymphatic system is by a 

 process of centrifugal growth from these centers. According 

 to Hoyer's ('08) account, a single vessel grows out dorsally 

 from the heart to divide into an anterior and a posterior 

 branch, the jugular lymphatic and the lateral body trunk, 

 respectively, each of which becomes distributed to its particu- 

 lar territory by repeated division and continued centrifugal 

 growth and adjustments. Though important changes are in- 

 troduced in the present account by substituting, in accord with 

 injections, the agency of a primary lymph-heart-plexus in 

 inaugurating the lymphatic system, and carrying out its dis- 

 tribution, Hoyer's essential principle of centrifugal growth 

 from centers associated with the lymph hearts is retained. 



The present contribution furnishes the lacking detailed pic- 

 tures and descriptions of a series of early injections, giving 

 fundamental relations of the first lymphatic plexuses and of 

 hearts subsequently developed in them, long needed to fill the 

 gap between the first stage and the relatively late modified 

 system illustrated in Hoyer's ('05) beautiful figures of the 

 late 26-mm. frog larva, R. temporaria, which have been ex- 

 tensively used for reference as the typical lymphatic system 

 for anuran larvae (text figs. D and E, p. 70). 



It is of decided value that injections of early stages now 

 give more completely the relations of the anterior lymph 

 hearts and their primary lymph plexuses to the segmental 

 systems of the embryo. Comparisons with urodeles and other 

 vertebrates are thus made easy before these relations are 

 obscured by secondary changes in late larvae. Kampmeier 

 has overlooked the statements just quoted, though he has 

 accepted as fact some features expressed in them, in his five 

 papers ('15-'25) on the development of lymphatics in toad 

 embryos by the method of reconstruction. 



