PLATE 31 



EXPLANATION OF FIGURE 



Fig. 41 Photomicrograph of a transverse section of a 15 mm. embryo of 

 Chelydra serpentina, taken through the periaortal lymph sinus; showing that this 

 endothelial-lined lymph sinus (25) is in direct and open communication with a typi- 

 cal mesenchymal-lined tissue space (26). Columbia Embryological Collection 

 (Col. of P. and S.) 317, slide 12, section 9. 



Fig. 42 Photomicrograph of a transverse section taken through the subocular 

 lymph sacs of a twenty-one-day rainbow trout embryo in which, as independent 

 structures, the sacs (1) have reached the maximum stage of their development. 

 P. E. C. 646, slide 1, section 70; injected embryo. 



REFERENCES 



6, Precardinal or jugular vein 

 20, Caudal end of eye 

 22, Carotid artery 



25, Periaortal lymph sinus of Chelydra 



serpentina 



26, Mesenchymal tissue space which 

 communicates directly with the peri- 



aortal lymph sinus of Chelydra ser- 

 pentina 



32, Mesenchymal tissue spaces which 

 lie in the line of extension of the 

 periaortal lymph sinus of Chelydra 

 serpentina 



136 



