PLATE 15 



EXPLANATION OP FIGURE 



Fig. 20 Photomicrograph of a frontal section taken through the anlagen of 

 the subocular lymph sacs (1) in a fourteen-day steelhead trout embryo. P. E. C. 

 696, slide 1, section 69; injected embryo. 



REFERENCES 



1, Subocular lymph sac 22, Carotid artery 



6, Precardinal or jugular vein 28, Infundibulum 



104 



