A STUDY IN MORPHOLOGY. 131 



Fig. 11. Optical section along the principal axis of a somewhat older egg, showing the 



yolk spherule, c, and the segmentation cavity, b. 

 Fig. 12. Optical section of the same egg at right angles to the one shown in fig. 11. 



b. The segmentation cavity. 



c. The yolk spherule. 



PLATE 2. 



Fig. 13. An optical section of an egg somewhat older than the one shown in fig. 1 1. 



Fig. 14. Optical section at right angles to that of fig. 13. 



Fig. 15. Optical section of an egg a little older than the one shown in fig. 13. 



d. Orifice of invagination. 



Fig. 16. Optical section of a still older egg in the same position as figure 15. 

 Fig. 17. Optical section of a still older egg in the same position. 

 Fig. 18. Surface view of the formative pole of the egg shown in fig. 17. 

 Fig. 19. Optical section along the principal axis of a still older egg. 

 Fig. 20. A similar section of a still older egg. 



Fig. 21. Ventral view of an embryo in the egg-shell 24 hours after oviposition. 

 c. Anterior end of body. 



f. Large spherules in the region of the digestive tract. 



g. Metastoma. 



Fig. 22. Dorsal view of the same embryo. 



(e and /as in fig. 21.) 



h. Cerebral ganglia. 



i. Pigment spots. 



m. Muscles. 



Fig. 23. Similar aspect of the same embryo artificially removed from the egg shell. 

 (Letters as in fig. 22.) 



PLATE 3. 



Fig. 24. Ventral view of the same embryo, seen from a point of view a little anterior 

 to that of fig. 2 1 . 



ex. Exopodite. 



en. Endopodite. 



(The other letters as in fig. 21.) 



Fig. 25. Side view of the Nauplius, r^foth inch long, as it leaves the egg 36 hours 

 after oviposition. 



g. Metastoma. 



p. Pigment spots. 



ex. Exopodite. 



en. Endopodite. 



