■ ■ ■ /,'. Sabin. 



_ .t certainty on the basis of many injections that the 

 jugular sac has .1 complete endothelial wall and is a closed vese 



I - ■ us 1 ear thai Kampmeier has uol de nstrated that this upper 



l>;in of the thoracic duct replaces degenerating reins. 



• 1 point, however, in Kampmeier's work is 1 1« » t that some 



nf tlie lymphatics replace degenerating reins, but that they develop 



out of tissue spaces. As the chief proof of this theon he uses .1 



onstruction of an injected specimen of mine. Notwithstanding the 



I that this injection is the only one which has yet been made in ;i 



mammal in this early stage, Kampmeier does not hesitate to call it 



I as ejected indirectly through the jugular lymph sac, 

 from which the injection mass ran into the thoracic duct. At a cer- 

 tain point in the injection there is an extravasation (Kampmeier, 

 fig. 13, line 15), and in exactly the same position in. the next section 

 large endothelial-lined empty space. 1: 1- therefore merely an 

 arbitrary decision whether the emptj vessel was actually connected 

 with the injected pari or not, thai is to Bay, there 1- as much evidence 

 for the one vie^ a- for the other. No one who has had experience with 

 tin- injection method would be sure thai the first injection in a new 

 region was a complete one. The spaces which Kampmeier has shown 

 as lymphatics in my specimen arc lined by endothelium; that is, 

 they are the spaces with which Lewis (76) has made us familiar; 

 they arc imt the mesenchyme spaces which Kampmeier and Strom- 

 sen regard as the anlage of lymphatics. 



Stromsen (146a) has injected the prevertebral lymphatics in turtles 

 ;iinl finds that in advance of the injected zone there arc enlarged 

 tissue spaces which he thinks arc going t<> become lymphatics. Kamp- 

 meier says that it 1- easy to select tissue spaces which are -nine to 

 become lymphatics for, "histologically, all incipient lymphatic an- 

 lagen, whether thej are spaces independenl in position or spaces fol- 

 lowing, transforming and expanding the discarded pathways nf 

 redundant \> uous channels, are decidedlj different from cither an 

 active vein or a mature lymphatic "' ( Kampmeier 66a, p. 130). Strom- 

 sen (1 16, p. 354) adds to this ability to select tissue spaces which are 

 going to become lymphatics tin- further point, that such enlarged tis- 

 .-11. c only in the pathwaj <<\' developing lymphatics. These 



two points can he easily disproved by anyone who has access to serial 



embryos. Km- example, why were nol the enlarged tissue 

 spaces in Kampmeier elected as lymphatics? <nn>i| examples 



