Hargitt: Pennaria tiarella and Tubularia crocea. 



Explanation of Plates. 



All Figures have been made with the aid of the Abbe camera lucida at a 

 projection distance of 450 mm. The various magnifications were secured 

 by the following combinations: X 2250, Zeiss 2 mm. apochromat. and com- 

 pensating ocular 12; X 1600, Zeiss 2 mm. apochromat. and compensating 

 ocular 8; X 51 Leitz objective 3 and ocular 4. The magnification is given 

 for each Figure. 



Abbreviations. 

 cl. pol, = polar cell. 



o'cy^. = oocyte, chromatin in dense mass. 



o'q^^. = oocyte, chromatin thread beginning; nucleolus present. 

 o'cy^. = oocyte, chromatin in a spireme. 

 o'go^. = oogonia before last division. 

 o'go'^. = oogonia in last division. 



PLATE 1. 



Pennaria tiarella. 



Fig. 1. Nucleus of egg from medusa killed 10 hours before time of libera- 

 tion, showing large eccentric nucleolus and chromatin reticulum. 

 Zenker, Conklin's picro-hematoxylin. X 1600. 



Fig. 2. Similar to Figure 1; the nucleus ovoidal: the nucleolus almost dis- 

 solved. Bouin's fluid, Ehrlich's hematoxylin and eosin. X 1600. 



Fig. 3. Germinative vesicle of egg immediately before liberation of the 

 medusa. Chromatin condensed into beads along the linin reticu- 

 lum. Nucleolus large and homogeneous. Bouin's fluid, iron 

 hematoxylin and Congo red. X 1600. 



Fig. 4. Similar to Figure 3. Chromatin only slightly condensed, and nucleo- 

 lus almost dissolved. Bouin's fluid, iron hematoxylin and Congo 

 red. X 1600. 



Figs. 5-7. Germinative vesicles from three eggs of the same medusa before 

 liberation, and just previous to polar-cell formation. Figures 5 

 and 6 possess cytoplasmic zones, but no asters. Figure 7 has 

 two centrosomes and asters, and the formation of the first matura- 

 tion spindle has begun. Bouin's fluid, picro-hematoxylin. 

 X 1600. 



Figs. 8a, 8b. Two consecutive sections. Nearly polar views of first matura- 

 tion spindle showing chromosomes in equator. Egg from same 

 medusa as that shown in Figure 4. A splitting of some chromo- 

 somes is indicated. Bouin's fluid, iron hematoxylin and Congo 

 red. X 2250. 



Figs. 9a, 9b. Another egg from same medusa in same condition as in Figures 

 8a, 8b. Some chromosomes in tetrads. Bouin's fluid, iron 

 hematoxylin and Congo red. X 2250. 



