PLATE 18. 



Fig. I. Bougainvillia niobc, Nassau Harbor, Bahamas, March 18, 



Fig. 2. Roiiaiilnvillla niobc, section ot a young medusa-bud upon the ecto- 

 derm of the manubrium. r, central mass of degenerating cells; 

 c < t, ectoderm of the manubrium of the parent medusa; c n t, 

 (brown) entoderm of the parent medusa; e c t b, (gray) ectoderm 

 of the budding medusa; e n t b, (green) entoderm of the budding 

 medusa; s I, limiting membrane between the ectoderm and ento- 

 derm of the manubrium ot the parent medusa. 



Fig. 5. Bougainvillia niobc. Cross-section of the medusa showing the 

 budding region of the manubrium. Successive stages in develop- 

 ment of buds are shown in hi b4. Colors as in figure 2. 



Fig. 4. R/it/iki'/i flea/ins, mature male. Tortugas, Florida, July I, 1899. 



Fig. 5. Rathkea octof>unct<it(i var. grata. Newport Harbor, Rhode Island, 

 April 24, 1897. 



Drawn by the author from living and preserved specimens. 



