696 GREENE. 



EXPLANATION OF PLATE XL? 



Fig. 13. Cross-section of a ventral organ at its first recognizable stage. Only 

 a slight aggregation of cells in the basal layer of the ectoderm has appeared. 

 This row is not associated with a lateral-line sense-organ Anlage. Embryo about 

 9 mm. long. 



Fig. 14. Cross-section of gastric organ associated with sense-organ Anlage, 

 J an. From the same embryo as Fig. 13. 



Fig. 15. Cross-section of a pleural organ of an embryo 14 mm. long. The 

 sensory Anlage shows to the left of organ. 



Fig. 16. Section of a gular organ just external to the base of the ventral fin. 

 Same embryo as Fig. 1 5. 



Fig. 17. An organ from the same region as Fig. 16, but associated with a 

 sense-organ. 



Fig. 18. A pleural organ slightly older but from the same embryo as Fig. 15. 

 s an, sensory Anlage. 



Fig. 19. An inner anal organ beginning to separate from the epidermis. Same 

 embryo as Fig. 15. 



Fig. 20. Section through a pair of anal organs, showing a different degree of 

 development. Same embryo as Fig. 15. 



Figs. 21 and 22. Organs in process of separation from the epidermis. Cora- 

 pare with Fig. 12. 



Figs. 23 and 24. Organs separated from the epidermis. The lens, /, and the 

 gland, ^/, are distinguishable, and the reflector, r, is forming from the connective 

 tissue. Pigment cells, /, are arranged around the outside of the reflector. 



