PLATE 19 



EXPLANATION OF FIGTJRE 



Fig. 25 Photomicrograph of a transverse section of a fourteen-day steelhead 

 trout embryo, taken at the level of the infraobital veins (23) ; showing that in 

 the course of their forward extension, the subocular lymph sacs have not reached 

 the level of the infraorbital veins. P. E. C. 696, slide 1, section 61 injected 

 embryo . 



REFERENCES 



6, Precardinal or jugular vein 23, Infraorbital vein 



20, Caudal end of eye 28, Infundibulum 



22, Carotid artery 



112 



