14 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



eral, at a time before lymphatico-venous valves have been 

 formed. This influx we have seen is largely accidental in trout 

 embryos and, even then, is practically only permissible in the ab- 

 sence of lymphatico-venous valves. In view of what has been 

 stated above regarding the subocular lymph sacs of the trout, and 

 the presence of blood in the lymphatics of vertebrates in gen- 

 eral (in relation to the absence of lymphatico-venous. valves) , it 

 is plain that the presence of blood in the lymphatics in no sense 

 indicates that the lymphatics of fishes are transformed veins, or, 

 that they are more closely related to the veins than the lymphatics 

 of other vertebrates. 



Miller ('13) and Huntington ('14) have applied the term 

 'haemophoric' to certain lymphatics of amniotes which convey 

 blood corpuscles developed in the adjacent mesenchyme to the 

 venous circulation. As far as I have been able to determine 

 haematopoesis does not occur in the trout and ganoids in relation 

 to the lymphatics of the head and pharynx. The influx of blood 

 from the veins into the lymphatics of fishes is, therefore, in no 

 sense comparable to what Huntington and Miller have described 

 as the ^haemophoric' function of the lymphatics in the em- 

 bryos of amniotes. 



IV. THE MODIFICATIONS WHICH THE EMBRYONIC GROUND-PLAN 



OF THE LYMPHATIC SYSTEM UNDERGOES IN ESTABLISHING 



THE MORE ADVANCED STAGES IN THE TROUT 



The lymphatic system as found in the head and pharjmx of the 

 twenty-two-day rainbow trout (fig. 10) represents a ground-plan 

 upon which that of the adult is necessarily built. I have not 

 followed in detail all of the transformations which lead up to the 

 adult condition, but have examined and reconstructed several 

 advanced stages in which the conditions cannot, in the main, be 

 unlike those found in the adult, and which are easily interpreted 

 on the basis of their origin from such a ground-plan. 



The modifications which this primary ground-plan undergoes in 

 subsequent stages of development are largely related: (1) To the 

 increasing importance gradually attained by the precardinal 

 lymphatics and their tributaries; (2) to the apparently complete 



