Plate 6. 



Development of Mnemiopsis leidyi. Agassiz Laboratory, Newport, 

 Rhode Island, July 27 to August 4, 1892. 



Fig. 20. Newly laid egg. 



Fig. 21. View of animal pole in a late segmentation stage. About 

 6 hours after egg is laid. 



Fig. 22. Side view of stage slightly older than figure 21. 



Fig. 23. View of vegetal pole of an embryo about 7 hoiu"s old, slightly 

 older than that shown in figure 22. 



Fig. 24. Side view of an embryo about 7 hours old. 



Fig. 25. First appearance of ciliary combs in 4 double rows. 



Figs. 26 and 27. Median sagittal optical sections to show arrangement 

 of cells. Ectoderm dotted and composed of many small 

 cells, individual cells not being shown in figure. Ento- 

 derm cells large and drawn in outline. 



Figs. 28 and 29. Development of concretions at aboral pole of embryo. 

 Figure 29 shows the same animal half -hour older than that 

 shown in figure 28. Note remarkable development of 

 dlia during the interval. 



Figs. 30-32. Oral, aboral, and side views of embryo about 3 hours 

 older than those shown in figvires 28 and 29. 



Fig. 33. Embryo still within the egg-envelope, about 24 hours old. 

 No tentacles have yet developed. 



Fig. 34. Embryo with tentacles, about 30 hours old and still within 

 the egg envelope. 



Fig. 35. Newly-hatched embryo about 30 hoiu-s old. The animal is 

 now in the Cydippidae-stage. 



Fig. 36. Aboral pole of an embryo about 32 hours old, showing de- 

 cided lateral compression, the tentacular axis being now 

 the wider, as in Mertensia, although the reverse is the case 

 in the matiire animal. 



Fig. 37. Side view of an embryo about 32 hours old, showing muscular 

 strands. 



Fig. 38. About 36 hotu-s old. View of aboral pole, showing a stage 

 wherein the stomodasal axis has become nearly as wide as 

 the tentacular. 



Fig. 39. Young Mnemiopsis leidyi, 5 mm. long. The oral ends of the 

 2 paragastric canals are now i-shaped, the 2 meridional 

 ventral canals of each side are fusing at their oral ends. 

 The tentacles are migrating downward toward the mouth 

 and the oral lobes are about to develop. 



Drawn from life, by the author. 



