52 CHARLES F. W. McCLURE 



thence to the veins. It is also significant to note that the endothe- 

 lium of the anterior lymph-hearts in the frog and toad from which, 

 by some investigators, the lymphatics are supposed to grow, is 

 not vitally stained by colloidal acid dyes. As a matter of fact, the 

 earliest stage of development at which the lymphatics react toward 

 these dyes in the frog and toad, is one not very far removed from 

 their permanent larval form. Such an advanced stage would not 

 ordinarily be regarded as a favorable one from which to infer in 

 what manner the lymphatics have been formed. 



The method of vital staining by colloidal acid dyes, like the 

 injection method as ordinarily used, does not therefore demon- 

 strate the existence of lymphatics in the embryonic body, until 

 their development is far advanced and until after continuous 

 channels are formed. This method, also like the injection method, 

 is incapable of demonstrating the early independent anlages of 

 the lymphatics, like those of the head sinuses in the frog and toad, 

 which at one time are entirely independent of each other and of 

 the veins (Chapter 11). 



The 'crucial test' referred to by Wislocki of the first and second 

 'views' therefore completely fails, as a vital staining of the lymphatic 

 tissues by his method is not possible at a time when such conditions 

 might arise. It would not be impossible, however, by this method 

 to follow the growth of lymphatics which may sprout from other 

 lymphatics. This would not prove, however, that such lymphat- 

 ics had grown out continuously and centrifugally from the veins. 



So much stress has been laid to the circumstance that lymphat- 

 ics grow into the caudal fin of the tadpole's tail, it may not be out 

 of place to discuss here more fully the real significance of this 

 observation. 



It must be borne in mind that Clark's ('09, '12) observations 

 are confined exclusively to the growth of lymphatic endothelium 

 in the caudal fin and that this endothelium does not grow into the 

 fin from the endothelium of a vein, but from that of another lymphatic. 



The circumstance that lymphatics grow into the tadpole's fin 

 from other lymphatics, has been sufficient proof, in the minds of 

 some, that all other lymphatics of the body must also originate 

 by growth and that their source of origin must of necessity be the 



