50 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



lymphatic/ it can be demonstrated that its anlage first appears 

 in the mesenchyme independently of the veins, and that a con- 

 nection between it and the veins is established secondaril}^ It 

 is highly improbable that homologous structures, like the sub- 

 ocular lymph sacs of fishes, could differ fundamentally in their 

 mode of development. We have seen that the subocular lymph 

 sacs of ganoids would be classed as 'venolymphatics,' on the 

 basis of the direct connections which they establish with the 

 veins in the immediate neighborhood of the sacs; the subocular 

 lymph sacs of the trout, however, could not be designated as 

 ' venolymphatics' on this basis, since they never communicate 

 with the veins in the neighborhood of the sacs. The develop- 

 ment of the subocular lymph sacs of fishes therefore serves as an- 

 other illustration of the fact that no distinction really exists be- 

 tween ' venolymphatics' and other anlagen of the lymphatic 

 system. 



XI. VARIATIONS IN THE RATE AT WHICH THE LYIMPHATIC SYSTEM 

 OF THE TROUT DEVELOPS IN DIFFERENT EMBRYOS OF THE SAME 

 AGE, AS WELL AS UPON OPPOSITE SIDES OF THE SAME EMBRYO 



It has already been stated that much variation exists in the 

 rate at which the lymphatic system develops in different indi- 

 viduals of the same age, as well as upon opposite sides of the same 

 individual. This variability has been partially illustrated in the 

 figures of the reconstructions, but is more fully borne out by the 

 following observations which were made in following the course 

 of the injecta in the lateral pharyngeal lymphatic of the living 

 embryo. In order to illustrate this variability more fully, I will 

 give the results observed in connection with a particular series 

 of steelhead trout embryos which were developed at a tempera- 

 ture of about 10.5°C and injected under the binocular microscope. 

 All injections were made through the caudal vein. 



In this particular series of trout embryos the lymphatic sys- 

 tem could not be injected until the fourteenth day after fertihza- 

 tion. On the fourteenth and fifteenth days after fertilization the 

 cardino-Cuvierian and otic lymph sacs could be injected in a few 



