38 HENRY MCELDERRY KNOWER 



published in the Proceedings in The Anatomical Record, 

 February, 1914. That report has since been fully confirmed 

 by many additional injections, which are considered in the 

 present paper. A quotation from this report of 1913-1914 

 (Knower, '13-'14) follows: 



4 'The first lymph vessels in the frog form a small and super- 

 ficial dorso-lateral plexus, which drains into the pronephric 

 sinus through a short vein (now identified as the third). On 

 this plexus in the frog .... the anterior lymph hearts ap- 

 pear later, at the point of entrance of the plexus into the veins 

 .... thus facilitating the emptying of the plexus into the 

 venous channels surrounding the excretory tubules .... the 

 endothelial lymphatic vessels carry off the accumulated prod- 

 ucts more directly and rapidly from the tissues than would be 

 possible through tissue spaces. It is our view that they can 

 thus be carried more rapidly to the pronephros for elimination 

 (see Abel, J. Pharm., 1912). The appearance of the first 

 lymphatics at this stage, and in the region of the body where 

 important physiological processes are being inaugurated, sug- 

 gests strongly that this association is causal .... As de- 

 velopment proceeds, the changes in the tissues bringing about 

 vacuolization, spaces, etc., progress tailward and take place 

 most actively just under the skin and dorso-laterally. Go- 

 incidentally, the lymphatic plexus travels backwards, spread- 

 ing dorsally and laterally beneath the skin .... In this 

 manner a delicate but rather extensive lymphatic plexus comes 

 to overlie the veins at the base of the tail before the appear- 

 ance of the posterior lymph hearts." 



These statements, based on uninjected specimens, are also in 

 agreement with the announcement of Knower ('08) here 

 stated : 



* 'When first found, the heart of each side lies over the poste- 

 rior end of the elongated pronephros, and empties into the 

 third (corrected number) intersegmental vein. The discovery 

 in Anura of this primary relationship of the anterior pair of 

 lymph hearts to the segmental vessels (veins) is of funda- 

 mental comparative value, bringing the hearts within the same 

 serial homology as the posterior hearts, and the more numer- 

 ous segmentally arranged hearts of Urodeles." 



