NO. 1783. NORTH AMERICAN LERN.EOPODID.E— WILSON. 225 



EXPLANATION OF PLATES. 



Platk 29. 



Fo7~mation and segmentation of the egg. 



Fig. 1. Section of oviduct, full of developing eggs, each with a cell filament attached 

 to one pole; b, coiled filament. 



2. A single, fully developed oocyte, with attached cell filament, more highly 



magnified. 



3. Division and migration of the germinal vesicle. 



4. The first cell of the germinal layer. 



5. The first two cells of the germinal layer. 



6. The germ layer forming into a blastoderm disk. 



7. Blastoderm disk half surrounding the egg. 



8. Completion of blastoderm disk and formation of blastoderm cuticle. 



9. Longitudinal section of nauplius larva, showing the beginnings of the 



appendages; a^ and a''^, first and second antennae; fg., frontal gland; m, 

 muscles which are to operate the swimming legs; md., mandible; mx^, 

 and mx^\, first and second maxillae; mxp., maxilliped; s^ and s^\ first 

 and second swimming legs. 



Plate 30. 

 Development ivithin the egg, nauplius stages. 



Fig. 10. Dorsal view of nauplius larva, freed from the egg membranes. 



11. Ventral view of same. 



12. Longitudinal horizontal section through a nauplius larva; a^ and a^^, first 



and second antennae; ab, fused genital segment and abdomen; fg., fron- 

 tal gland; lb., labrum; md., mandible; w., body wall. 



13. A section through the peg end or origin of the attachment filament; a/., 



attachment filament; /gr., frontal gland; p., peg. 



14. Attachment filament in two stages of growth; a, curved; b, cork-screw 



shaped. 



15. Side view of fully developed metanauplius within the egg. 



Plate 31. 



Development within the egg, metanauplius stage. 



Fig. 16. Ventral view of metanauplius larva, freed from the egg membranes; a^ 

 and a^', first and second antennae; md., mandible; mxf . and mx^\, first 

 and second maxillae; mxp., maxilliped. 



17. First and second antennae enlarged. 



18. A diagonal longitudinal section through the body of a fully developed 



metanauplius coiled inside the egg membranes; lettering as in fig. 

 9 with these additions: af., attachment filament; e, rudimentary eye; 

 lb., labrum; ms., mesenteron epithelium forming over ventral surface of 

 the stomach; pg., paragnath. 



19. The second maxillae and the attachment filament of the second copepodid 



stage, showing the claws of the maxillae imbedded in the end of the 

 filament. 



20. A single maxilla with the claw pried out of the filament. 



21. Tip of maxilla and claw enlarged. 



Proc.N.M.vol.39— 10— 17 



